This page has a general collection of information on catastrophic volcanos worldwide, and catastrophic earthquakes in the U.S. It isn't quite a total compendium; for instance, I have nothing on the threat of one of the Canary Islands collapsing and generating a tsunami to swamp some or all of the American east coast, because, whatever else it is, that threat is very easy to understand. Other threats like those posed by Yellowstone and the Long Valley Caldera are harder to follow.
For geological, seismological, and tectonic terminology, see Dora the Explorer's Earthquake Page
Yellowstone Park is volcanically active. This is what causes the geysers. Under Yellowstone Park is a culdera volcano that blows catastrophically every 600,000 to 700,000 years. It last blew 600,000 years ago, and there has been uplift under the caldera, indicating the buildup of pressure. There is serious controversy about whether that means there is an actual need to attend to this. If it blew, it would wipe out all life in Wyoming and possibly surrounding states, and seriously damage Earth's weather for some years.
A caldera volcano is an especially violent form of volcano. The volcano on Santorini, in the Mediterranean, for instance, is a caldera volcano. They are covered by layers of hard magma and other rock. Over time great pressure builds up under the lava dome. Gas forms - but remains dissolved in teh magma because of the great pressure. If something cracks part of the crust, and especially if water gets into it, which does not happen only in an ocean or sea, magma can escape. Then the pressure lessens, the gas undissolves, and the entire caldera blows sky high, usually in a truly catastrophic volcano, though there are small culdera volcanoes like Mt. St. Helens. The lava dome collapes; leaving a big crater that often becomes a lake. The explosion of Santorini in about 1500 BC caused the plagues of Exodus, and more dramatic tidal waves all over the Mediterranean, catastrophically changed the climate in China for 15 years, left ash in Greenland, and destroyed Cretan civilization. The last volcano as violent as the one under Yellowstone was Mt. Toba, on Sumatra (a hundred miles east of the recent catastrophic earthquake), which caused severe planet wide weather changes and brought the human race to the within about a hundred individuals in East Africa of extinction.
The reason for such a hot spot in Wyoming is a hot spot. A hot spot is a weakened area in the Earth's crust that magma flows through. Hot spots move over time, and Yellowstone's has left a lengthy track of having moved from the border of Oregon. The Hawaian Islands are another well known hot spot. As the hot spot moves, old parts of the island chain erode away and new islands are born. However, the Hawaian volcanoes are among the least explosive volcanoes on earth. It all depends on whether the structure of teh volcano lets magma escape easily, as well as on the type of magma.
BBC/ PBS Horizon Special: Supervolcanoes - Transcript and Web Site Describes supervolcanoes like Krakatoa, Toba and the caldera volcano under Yellowstone Park, which erupts catastrophically every 600,000 to 700,000 years, last erupted 600,000 years ago, is still alive, accounts for the geography and geological activity at Yellowstone Park, and has recently been uplifting.
transcript of the BBC Horizon Supervolcanoes program
Wikipedia article on the Yellowstone Supervolcano
The Snake River Plain and the Yellowstone Hot Spot
Wikpedia article on the Snake River Plain
Yellowstone: Another hot spot
Hot Spots and Mantle Plumes
When Yellowstone Explodes National Geographic web site, August 2009. Summary of history. There are graphics of the movement of the hotspot that underlies Yellowstone, and the trail of supervolcanic eruptions across the Snake River Plain.
Yellowstone Interactive on "When Yellowstone Explodes" web site - suggests that the hot spot may have been born of the subduction fault at the plate boundary, then the plate has moved over it, resulting in a 13 to 18 million year trail of supervolcano eruptions. The magma chamber has been drawn out in a more horizontal direction than it originally had as plate movement drags the volcanos away from the hot spot. Shows the date and location of each supervolcanic eruption.
Yellowstone Volcano Observatory web site Pay attention to the link about a slightly larger earthquake in the park early in 2008 - the page it links to tells us that earthquake activity in the park has been increasing, and also that a flurry of small quakes around the caldera was set off by a major quake in Alaska in 2002.
Volcano Monitoring at Yellowstone National Park
USGS Professional Paper 1717. Integrated Geoscience Studies in the Greater Yellowstone Area—Volcanic, Tectonic, and Hydrothermal Processes in the Yellowstone Geoecosystem. Collection of articles.
Monitoring a Supervolcano in Repose: Article in Elements Journal February 2008
Unusual large number of minor quakes in Yellowstone, end December 2008 Now, that is recent quakes in the Intermountain West, so maybe preserving today's map of recent earthquake activity would be helpful. Don't misinterpret the map as I initially did - the area outlined in red is the caldera, not the earthquake zone! The earthquake zone is shown by the little yellow squares and the big blue squares clumped around the northern end of the lake. The bulge was first noticed around the lake but is actually centered just northwest of the lake and again at the western end of the middle of the caldera. Below is a deformation velocity map showing how much the ground is deforming (bulging) where and in what directions. At its center the bulge bulged upward about 30 inches between the 1920's and the 1970's, according to Bob Smith's repeat of the 1920's geological survey. (I thought the greatest bulge was around the northern end of the lake where recent spate of earthquakes has been in December 2008 but apparently that is wrong.)
For comparison, here is a map of the Yellowstone caldera.
Here is a current (Dec 2008) US News and World Report article about the spate of quakes.
Yahoo news article on the quakes' normalcy:
However, earthquakes over time have not been concentrated over the northern end of the lake. But the Yellowstone observatory does not map the earthquakes over time, only by year. A page of links to those individual yearly mappings of quakes in Yellowstone is here. It looks to me rather like they fluctuate back and forth between the top of the bulge and its sides and edges, and there are several other centers of earthquake activity nearby. The land is not deforming in those areas. however. 2002 was a particularly busy year, but almost half the quakes were in November and December, and apparently a major quake in Alaska set them off.
Yellowstone at a Glance downloadable poster of graphics - viewable online - by University of Utah Seismology and Active Tectonics Research Group very revealing about dynamics of the rise and fall of the land in the area. (suggests cyclic rise and fall of land between caldera and mountain range just north of it), also tracks probable trail of the hot spot eruptions over 16 million years
Hughes, Scott, et al. Majfic volcanism and environmental geology of the eastern snake river plain, Idaho
Neogene Snake River Plain-Yellowstone Volcanic Province - Digital Geology of Idaho, with links to references
Digital Atlas of the Snake River Plain
USGS Yellowstone Volcano Observatory: Volcanic History of the Yellowstone Plateau Volcanic Field
Robert Christianson, The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana
USGS Yellowstone Volcano Observatory Path of the Yellowstone Hotspot
USGS Yellowstone Volcano Observatory Areas of the United States that once were covered by volcanic ash from Yellowstone's giant eruptions
Discovery News: Old Supervolcanoes Give Yellowstone Clues by Larry O'Hanlon
Discovery News: Yellowstone Depths Reveal Rock Plume
Is The Forecasting Of The Eruption Of The Yellowstone Supervolcano Possible? Robert B. Trombley, Ph.D.
U.S. Geological Survey Fact Sheet 2005-3024 2005 Steam Explosions, Earthquakes, and Volcanic Eruptions—What’s in Yellowstone’s Future?
Yellowstone's Super Sisters. Includes Toba, Taupo, Valles and Long Valley, and supervolcanoes on Jupiter's moons.
Yellowstone's Plumbing Reveals Plume of Hot and Molten Rock 410 Miles Deep New study finds plume is larger and deeper than previously thought. 20% larger to be precise. It is angled. The most significant piece of evidence, however, is proof that there is a hotspot, which sure expands the plume for those who believed that none existed! Probably they still believe none exists. Related papers find that the magma is cooler than expected, and that the caldera is rapidly refilling, or maybe "recharging".
Under Yellowstone, Magma Pocket 20% Larger Than Thought. Richard A. Lovett. National Geographic News. December 15, 2009. Huge Magma Pocket Lurks Beneath Yellowstone Supervolcano Ker Than. National Geographic Daily News. December 18, 2013. Yellowstone magma reservoir much larger than once thought. Specifically 55 miles by 20 miles (90 x 30 km on each side and 6 miles (10 km) deep. Yellowstone,s magma reservoir is not arranged vertically, as once thought, it's tilted in a northwest to southeast direction. The current magma reservoir is roughly equal to what it was when the supervolcano last erupted, about 640,000 years ago. Each time the magma reservoir is emptied, it takes a long time for it to refill again. When the volcano does erupt it will have global consequences. Ashfall as far away as the Great Plains, even farther east.
Yellowstone Plume, Hotspot, and Wasatch Front Earthquake Research University of Utah Tectonics and Active Seismology Research Group papers on Yellowstone Caldera - the papers referenced above.
Super Volcano Trigger Found This article discusses how caldera volcanoes erupt. I strongly doubt there is just one cause. According to this article in Discovery News, the dome that forms over the calderas of these volcanoes needs to be flexible for anything to happen. It swells and swells for very long periods of time, until eventually cracks form in the surface. Then the cracks grow, Eventually the cracks get big enough to cause the dome to collapse, triggering the eruption. This article says that unlike smaller volcanos, caldera eruptions are not triggered by smaller eruptions within the volcano. Thie theory predicts that the Yellowstone volcano is a long ways from erupting, because cracks would have formed and be getting bigger if an eruption was imminent.
Yellowstone Supervolcano Eruptions More Frequent than Thought? (Yellowstone Super-Eruptions More Numerous Than Thought?) Richard A. Lovett for National Geographic News. This National Geographic article presents findints that Yellowstone eruptions are more frequent than thought. There is evidence that the last major eruption 640 thousand years ago was several eruptions, and that two other eruptions have occurred since.
Yellowstone had Bulged as Magma Pocket Swells January 2011 National Geographic online. Since 2004, the ground above the Yellowstone Caldera has risen upward ten inches, as much as 2.8 inches a year. While the greatest growth occurred between 2004 and 2007, and the rate between 2007 and 2010 is a centimeter a year, the ground is continuing to rise. (Between 1923 and 1973, the ground rose 30 inches - but subsided - totally? in 1985.)
Reference to Yellowstone-supervolcano study in June 2012 issue of journal Quaternary Geochronology.
Supervolcanoes that could destroy humanity 'may explode sooner than scientists thought' Cites PLOS article end May 2012, reporting on research that found that large magma pools can only exist for a short time before eploding. Yellowstone's magma pool would then be recent.
Timescales of quartz crystallization and the longevity of the bishop giant magma body. Guilherme A. R. Gualda et al. PLOS One. May 30, 2012. They specifically find that the Bishop Tuff giant magma body, which erupted 760,000 years ago and created the Long VAlley caldera in California, took 500 to 3,000 years and not more than 10,000 years, to form, rather than more than a hundred thousand years. They base this on the process of quartz crystallization. They also argue that quartz in magma crystallizes differently than previously belived.
Yellowstone Supervolcano Discovery - Where Will it Erupt? New study finds fault lines most likely to produce next eruption. Richard A. Lovett, National Geographic News. September 20, 2012. Yellowstone's next major eruption will probably be centered in one of three parallel fault zones running north-northwest across the park, a new study predicts. Two of these areas produced large lava flows the last time the supervolcano was active—174,000 to 70,000 years ago—while the third has had the most frequent tremors in recent years. The hotspot also has smaller eruptions with thick vicious slow moving lava that flows, rather than exploding. Lava analysis shows that the magma in the lava flows rose very quickly form a magma chamber 4 to 7 miles deep. The titanum within the lava's quartz crystals marks the depth at which the crystals formed out of the slowly cooling magma. The speed at which the magma rose during its ascent did not change; the crystals did not have time to do more cooling at some points. Ben Ellis notes that eruptive patterms can change unexpectedly.
This is only here because it was mentioned in Dinosaur Planet and could confuse people. It may also have been mentioned by Horner in a book about a field or petrified forest of dead dinosaurs. It is an ancient, long dead, volcano. It happened to be one of the earliest ancient supervolcano calderas that was found, or something, and the fact that the distinctive ash from this volcano affected dinosaurs fifty miles away impressed researchers. Actually, there are quite a number of long dead supervolcanoes in the west and midwest; the Rocky Mountain and basin and plain area is actually among other things built on volcanic ground. Long ago it must have been a very interesting place. Researchers are barely sure a caldera is actually there! One other thing - this was the Elkhorn mountain range in Montana, not the harmless Elkhorn mountain in Idaho. Apparently there are eight million geographical features in the west named Elkhorn.
From Little Das' Hunt, Dinosaur Planet. Scott Sampson, Uath Museum of Natural History, "Descovery Quest Paleontologist".
"In a remote corner of Northwestern Montana, scientists unearthed a baffling mystery. The carred bones of dinosaurs. Based on the undisturbed state of the bones, it was concluded that the animals died on the spot. But what killed them?
"...The bones were found among more than 200 petrified trees all found under as much as 6 feet of cinder and ash. In turn, the trees lay within a field of ash covering 9600 sq. mi., one of the largest fields of volcanic ash in the world. Sometime in the late Cretaceous, about 75 million years ago, the forest was destroyed by a powerful volcanic eruption. The trees were leveled by the sheer force of the blast, then buried under a column of ash, along with the dinosaurs. [The Mt. St. Helens eruption in the 1980's produced similar destruction.] Yet the Elkhorn eruption ranks as one of the most powerful ever recorded. By comparison Mt. St. Helens was a mere firecracker".
The storyline is placed when the Rocky Mountains were young volcanic mountains. The Elkhorn Range of Mountains of Montana had rich volcanic soil. The collapse of the Eastern face of the volcanic mountain fueled the blast. The ash plume extended 300 miles from Montana to the inland sea of North America. The dinosaurs the storyline depicts as killed by the pyrochlastic flow lived 50 miles from the eruption.
Roberts, Eric et al, Taphonomy of a petrified forest in the two medicine formation (Campanian), Northwest Montana (This article is available from this source for $15.)
Dixon, Ron, Geology of the Elkhorn Mountains: Volcanics in the Southern Bull Mountain Area
"Approximately 77 million years ago, southwest Montana was the home of an active volcanic complex. The Elkhorn Mountains Volcanics (EMV), as they are now known, once contained one of the largest ash-flow volcanic fields on earth. This volcanic material once covered an estimated 10,400 square miles (26,000 km2) to a depth of approximately 2.5 miles (4.0 km). By comparison, the Yellowstone National Park volcanics are estimated to cover only 4,000 square miles (10,000 km2) to a depth of 500 feet (150.0 m). The EMV are Cretaceous in age "
This Wikipedia article on the Elkhorn Mountains discusses the Elkhorn Mountain Volcanics.
This Wikipedia graphic on late Cretaceous geography will amaze you. Apparently because the sea level was high, most of the central and southeastern United States was covered by water.
Geological posters of historical geological processes of the Western United States
Another large active caldera volcano is located on the eastern edge of the Sierra Nevada mountains, in California, near the Nevada state line. It too is being closely watched, because it is even more active than Yellowstone. It is very similar; with hot springs, rising bulges, and its last catastrophic eruption, which was on a scale similar to Yellowstone's, was about 700,000 years ago. Like Yellowstone it has also erupted more recently and less catastrophically. It is actually a little more dangerous than Yellowstone because it is on active major faults that regularly get moderately strong, 6.0 to 7.5 quakes, that are tied to the San Andreas fault system, and because in addition to uplifting it has been emitting toxic gas which is killing plant life in parts of the caldera. The region the volcano is on is being actively pulled apart by the tectonics of the area, as well as being tied to the San Andreas fault system.
Yellowstone's Super Sisters: Long Valley, California
Wikipedia article on Long Valley Caldera
Geomorphology from Space: Plate T-4: Tectonic history of the southwest
Mammoth Lake Shakes and the Earth Moves. Somewhat speculative but good maps of immediate region, good quake maps of southern California, good quake history of Mammoth Lakes area. Some history of the caldera.
What Shakes Mammoth Lakes? Ron Morris.
Current activity of Mammoth Lakes area by USGS
USGS fact sheet: Living with a restless Caldera -- Long Valley, California (Revised version)
USGS fact sheet: Future Eruptions in California's Long Valley Area -- What's Likely?
Long Valley Caldera and Mono-Inyo Craters Volcanic Field, California
USGS Long Valley Observatory: Geologic History of Long Valley Caldera and the Mono-Inyo Craters volcanic chain, California
USGS Volcano Hazard Program: Long Valley Observatory web site
Volcanoes of teh World: Long Valley Caldera: Western U.S. - California
The Case of the Missing Moho. September 23, 2004 - the southern Sierra Nevada have lost their boundary between crust and mantle.
The Geological Society: Geology News. A bad case of the drip steals geologists’ Moho September 2, 2004
Sierra Nevada unmoored - whoops! They not only lost their bottom and are tilting downward toward the west, raising the eastern edge, but they crumpled into the San Andreas fault and they're headed north! (Other versions of that are that the microplate the Sierra Nevada mountains sit on is turning counterclockwise, pulling the lower right quadrant where Long Valley is apart, and compressing the mountains in the other quadrants.)
Active foundering of a continental arc root beneath the southern Sierra Nevada in California George Brandt et al.
Supporting information for: Active foundering of a continental arc root beneath the southern Sierra Nevada, California. George Zandt, et al.
STRUCTURAL NATURE OF A LARGE DISCONTINUITY IN THE SIERRA NEVADA EXTENSIONAL FAULT SYSTEM: THE COYOTE "WARP" OF NORTHERN OWENS VALLEY, CALIFORNIA DAWERS, Nancye H., Department of Geology, Tulane University (Abstract)
The North American Tapestry of Time and Terrain: Garlock Fault
Birth of a fault: Connecting the Kern County and Walker Pass, California, earthquakes
Volcanism along the eastern Sierra Nevada frontal scarp
Transtensional model for the Sierra Nevada frontal fault system, eastern California. Jeffrey Unruh et al.
Basin and Range province
Geologic Provinces of the United States: Basin and Range Province
The Formation of the Rocky Mountains
USGS: Geologic Provinces of the United States: The Rocky Mountain System
Geology 33: Environmental Geomorphology: Major Geomorpo-tectonic Regions
Geo 1002: Earth History. Lecture 38: Tectonics of the Rocky Mountains
The Valles Caldera was a supervolcano, within the past 15 million years; but it is now dead. It is part of a completely failed rift valley in the southwestern United States, that has no apparent tectonic life left in it. The only reason for concern is that the extensional forces pulling the southern central and Western United States apart could conceivably some day reawaken the rift, which would be a ways away from reawakening the caldera.
Jemez, New Mexico. Jemez Volcano Field. Valles Caldera
Yellowstone's Super Sisters: Valles Caldera, New Mexico
The Rio Grande Rift By Steven Wade Veatch The Rio Grande Rift, home of the Valles Caldera, is a failed rift valley in New Mexico, produced by forces that continue to pull apart the southwestern United States.
USGS: The Rio Grande Rift
Rio Grande Rift GO 568 Structural Geology James S. Aber
Rio Grande Rift, Paul F. Ciesielski, University of Florida
Wikipedia article on La Garita Caldera
It was much larger than Yellowstone, part of a series of eruptions of its kind in the western U.S. 40 to 25 million years ago, and erupted a number of times over a million and a half years.
The Columbia River flood basalt is a key part of the geology of the western U.S., including the Snake River Plain. It was created about 14 million years ago of rift dynamics that apparently are dead.
See discussion at bottom of the page, "Fissure Eruptions". and "Columbia River Flood Basalts"
USGS page on Columbia River Basalts and other northwestern U.S. geological features.
This link appears to suggest a possible relationship between the Columbia River Flood Basalt and the Cascade Subduction Zone, though the flood basalt is supposed to have been created by rifting. Remarkable volcanic dynamics go on behind subduction zones, but that is what the Cascade range is about.
USGS Continental Flood Basalts gives geological and some minerological specifics on the region. Including the Snake River plain. It also discusses similar basalt flood zones elsewhere in North America. I have seen the Columbia River Flood Basalt linked to rifting in Iceland.
Overview of the Geological Provinces of California
USGS Description of the San Andreas Fault
USGS map of the most important fautls of California. Shows the Owens Valley Fault as a more or less continuous line connecting with the Garlock Fault, connecting with the Nevada border. Both this and map below say last major rupture was 8.0 in 1872 though local quake maps show earthquakes of mag 6 to 7.5 all around the Long Valley area.
Faults of Southern California main map
Southern California Earthquake data center: Faults of Southern California: Basin and Range Region. Shows teh Owens Valley Fault System as a group of faults northward along teh Sierra Nevada Fault system.
USGS Quaternary Faults and Folds by State and Region Manages to leave off the faults around Mono Lake
USGS Quaternary Faults and Folds Interactive Viewer Using this system, I was able to show that the Owens Valley Fault runs from the Garlock Fault to immediately south of Long Valley, where a linear set of little fault systems pick up and run through Mono Lake. There is also a circular group of faults at the top of the Owens Valey Fault zone called the Volcanic Tablelands faults. The northernmost segment of the Owens VAlley Fault, tha tends at teh Vlocanic Tablelandws, is the Keough Hot Springs section. The next segment is th fault zone that fractured in 1822 - or 1872?
EARTHQUAKE FAQ: UNITED STATES EARTHQUAKES Unusually clear page from UT Austin Institute for Geophysics - they say that California is prone to maximum 8.0 earthquakes, and since these quakes ordinarily occur every 60 to 100 years, and the last one occurred in 1906, another one is about due - or it might not occur for a century.
While the highest probabilities for large tsunamis on the U.S. coast consist of faults and geologically unstable terrain in Alaska, along the coast of the Carolinas, and a volcanic mountain in the Canary Islands, and while the liklihood of a major quake in California is well known, another, possibly bigger problem lies in the Missippi River VAlley in the area of MIssouri and Arkansas. In 1811-1812, a quake of magnitude 7 to 9 occurred near New Madrid, Missouri. The quake caused buildings to collapse and big holes and rifts to open in the earth, caused big tidal waves on the Mississippi river, caused cliffs and bluffs near the river to collapse, temporarily reversed teh flow of the Missippi River, and created a large new lake nearby. The quake caused church bells to ring in Boston, Massachusetts. Recently the area has been seismically active again, with hundreds of quakes up to magnitude 2 a year. There has been concern about the possibilty of another big quake. Today such an event would kill a large number of people and inflict great economic damage.
The greater part of the damage was actually caused by the fact that much of the north central and northeastern U.S. is covered to a great depth by packed rock and sand. The quake caused this stuff to "liquefy" and collapse in many places.
The quake itself was caused by a failed continental rift under that part of the Mississippi River Valley. Shortly before Africa and Europe were separated from the Americas, by the formation of the Atlantic Ocean basin, a seismic rift formed in the Mississippi VAlley, with associated volcanism. Lava flowed from the rifting and formed big hunks of igneous rock along the fault lines. Recently some sort of pressure on the North American continent from both East and West has reactivated the fault zone.
Major quakes have occurred there repeatedly in the past and will occur again though no idea if one will happen any time soon.
Below are some links to information about the fault zone.
Wikipedia article on the New Madrid Earthquake
Wikipedia article on the New Madrid Seismic Zone
TheVirtual Times: The Great New Madrid Earthquake
Southern Illinois University Department of Geology: Earthquakes and the New Madrid Seismic Zone
Rockhounding Arizona: Your Fault, My Fault, and the New Madrid Fault
Source Mechanisms of Earthquakes in the Eastern North America (1976-1996) - a map of large earthquakes in the eastern U.S. in this time period.
Map of earthquakes Recorded in the Eastern U.S. in 1995-98
USGS Areas of Quaternary deformation and liquefaction, New Madrid region, central Mississippi River Valley
USGS Areas of Quaternary deformation and liquefaction in the Mississippi and Ohio Rivers region
USGS Areas of Quaternary and historic liquefaction, coastal North and South Carolina
USGS Seismic hazard map, Conterminous U.S.A. Think the Bush "scientists" got at this page. In theory it still exists but they seem to be too interested in gobbledygooking it to let one get to it. Here is the U.S. Seismic Hazards Map link.
Scientific Probabilities of a major quake in the San Madrid Fault Zone.
New Madrid Earthquake map
New Madrid Seismic Zone: Graphics, Maps, and Information
1812 Madrid earthquake information.
Map of New Madrid Fault Zone
The Mississippi Valley - "Whole Lotta Shakin' Goin' On
Uncovering Hidden Hazards in the Mississippi Valley
Shake Rattle and Roll: The New Madrid Fault Past and Present
NCSA: Shake, Rattle and Roll - about the characteristics of a recent earthquake in Illinois.
Reelfoot Rift (More on the geology of the central United States)
The Cascadia Megathrust and Tectonic Stress in the Pacific Northwest
Pacific Northwest Seismograph Network: FAQS on Pacific Northwest Earthquakes
Map of volcanism in the Pacific Northwest - shows the arc of volcanic mountains adjacent to the Snake River Plain adjacent to its eastern edge.
Cascadia (Pacific Northwest) Seismicity: William P. Leeman, Tsunami!
National Geographic News: Did North American Quake Cause 1700 Japanese Tsunami?
The Earthquake Threat in Southwestern British Columbia John J. Clague Department of Earth Sciences, Simon Fraser University This is a very good review of the research and the various threats that earthquakes in the region pose.
Recent Earthquake Information for Canada
SEISMIC ZONING MAP OF CANADA, 1985: ACCELERATION (NBCC)
Earthquake Zones in Eastern Canada (see Charlevoix Seismic Zone halfway down page, and Lower St. Lawrence seismic zone three-quarters down page)
List of recent Canadian earthquakes
Geocscape Quebec: The Earth Shakes Under Quebec
EARTHQUAKES IN THE CHARLEVOIX-KAMOURASKA SEISMIC ZONE
Paper No. 88-0 SUPRACRUSTAL FAULTS OF THE ST. LAWRENCE RIFT SYSTEM, QUEBEC: KINEMATICS AND GEOMETRY AS REVEALED BY FIELD MAPPING AND MARINE SEISMIC REFLECTION DATA
Paper No. 35-10 SUPRACRUSTAL FAULTS OF THE ST. LAWRENCE RIFT SYSTEM, QUEBEC: KINEMATICS, GEOMETRY AND AGE AS REVEALED BY FIELD MAPPING, MARINE SEISMIC REFLECTION AND FISSION TRACK DATA
The Geological Regions of Quebec
See explanation of glacial rebound on page 1.
The Canadian Shield
Reality bytes: Canadian Shield
Quebec City - geological tour
Cooling and the Laurentian ice sheet
The rocks of the Quebec City area: an entire world beneath our feet
The Teays River (ancient river system that drained northeastern North America)
Teays River - Wikpedia
Canadian Shield, Precambrian Shield or Laurentian Plateau
The Architecture, Origin and Evolution of the Paleozoic Continental Margin of Laurentia: Geometry and origin of supracrustal faults of the Charlevoix area, Quebec Abstract.
Crustal strain rates and seismic hazard from seismicity and GPS measurements along the St Lawrence Valley, Quebec. Abstract
Geological Provinces of Canada
The Natural Topography of the Great Lakes - St. Lawrence Region
Seismotectonic characteristics of the Lower St. Lawrence Seismic Zone, Quebec: insights from geology, magnetics, gravity, and seismics (abstract). Maurice Lamontagne, Pierre Keating, and Serge Perreault Can. J. Earth Sci./Rev. Can. Sci. Terre 40(2): 317-336 (2003)
The Charlevoix Meteorite Crater
Charlevoix Meteorite Crater - Wikipedia
Revisiting the geological structures of the Lower St. Lawrence Seismic Zone, Quebec: Insights from magnetic, gravity and seismic data
Superficial Geology from the Hudson Valley to the Massachusetts Coast
The Atlas of Canada: Geological Provinces
Interactive Map of Canadian Shield
A Forest Primeval: A primer on the great forest of the Adirondacks.
The Adirondack Mountains: New Mountains From Old Rocks
Basic Geology and Neotectonics of the Adirondacks
http://www.geo.www.edu/~tsattler/tectonics/adirondack/mountains.html - old link that no longer functions.
A Short Geological History of the Northeastern United States
Geology of the Lake George Region and the Adirondacks
Grenville Event and Virginia geology
The Appalachian System
Tectonics of the Southern Appalachians
Geologic History of the Appalachian Mountains
The Appalachian Mountains and Plate Tectonics
Missing Oceans and Colliding Continents: A Field Trip Guide to the Appalachian Mountains: Quebec City to Maine
Geologic Events of the Carolinas and Beyond
Tectonics of the Appalachians
Northeast Geologic History
The southwestern edge of the ring of fire is so tectonically complex and unstable that it is actually home to more than weekly earthquakes. Sumatra has been home to some doozies. Other catastrophic volcanoes in relatively recent history have occurred in other parts of Indonesia and in the Philippines. The following were all a good deal larger than Mount. St. Helens.
Volcano Live "Supervolcanoes"
Toba volcano, Sumatra, Indonesia This catastrophic volcano around 75,000 BCE, give or take 10,000 years, is discussed in the Supervolcanos program above. It buried southeast Asia under a layer of ash, caused a severe volcanic winter that may have lasted a thousand years, and helped trigger an ice age. It left a permanent volcanic lake and island in the mountain range on northern Sumatra. This is a recurrent caldera volcano like that at Yellowstone - and scientists do not know if it is done with its cycles of erupting. It brought the human race, previously spread through Asia and Europe, to within a hundred individuals of extinction, which resulted in a serious genetic bottleneck. Humanity should be far more varied and its genetic variation far older than it is - as measured by mitochondrial and Y chromosome DNA, which change between generations only by a slow rate of mutation. The age and degree of genetic variation suggest that 65,000 to 85,000 years ago the worldwide population of humans shrank to between 1,000 and 10,000 reproducing adults (5000 is an often quoted figure). In other words, we came close to preceding Neanderthals into extinction. Though there is archeological evidence that humans lived in Indonesia when the eruption occurred, as evidence of them was buried in the ash, the genetic evidence (of a spread of existing genetic diversity from Africa) and geographical logic (people in Africa were less affected by the eruption and by the resulting catastrophic climate changes) suggests that all of the long term survivors of the eruption whose descendants are living today, were in Africa when the eruption occurred and probably for atleast a thousand years thereafter. Neanderthals were established in Europe and survived there until 35,000 years ago (possibly eliminated by contact and competition with modern humans), but because ice age deserts stood in the way, modern humans did not reach Europe until 45,000 years ago.
Yellowstone's Super Sisters: Toba, Sumatra
This article excerpt explains clearly and concisely what happened. Late Pleistocene human
population bottlenecks, volcanic winter, and differentiation of modern
Note that several popular works by population geneticists claim that there is archeological evidence that arguably shows that some people who were in Indonesia at the time survived the eruption. However, proof that there were people in Indonesia at the time does not couple with proof that the oldest people out of Africa went through Indonesia on their way to Australia, to prove that they are descendants of people who lived in Indonesia when the eruption occurred and survived it. Even mitochondrial DNA analysis of remains that old from Indonesia might not conclusively prove it, but none has been offered.
The Toba volcano was the largest eruption in the past two million years - it beat the Yellowstone supervolcanos, which were more recent.
Toba, Sumatra, Indonesia. Oregon State University volcano web site.
Toba caldera produced the largest eruption in the last 2 million years. The caldera is 18 x 60 miles (30 by 100 km) and has a total relief of 5,100 feet (1700 m). The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff. The Young Toba Tuff was erupted from ring fractures that surround most or all of the present-day lake.
Comparison of volumes produced by some of the greatest volcanic eruptions. The Young Toba Tuff has an estimated volume of 2,800 cubic kilometers (km) and was erupted about 74,000 years ago. The Huckleberry Ridge Tuff, erupted at Yellowstone 2.2 million years ago, has a volume of 2,500 cubic km. The Lava Creek Tuff, erupted at Yellowstone 600,000 years ago, has a volume of 1,000 cubic km. The May 1980 eruption of Mount St. Helens produced 1 cubic km of ash. Not shown is the Fish Canyon Tuff of the San Juan Mountains of Colorado. The Fish Canyon Tuff was erupted 27.8 million years ago and has an estimated volume of 3,000 cubic km.
The volume of the youngest eruption is estimated at 2,800 cubic km, making the eruption the largest in the Quaternary. Pyroclastic flows covered an area of at least 20,000 square km. Up to 1200 feet (400 m) of Young Toba Tuff is exposed in the walls of the caldera. On Samosir Island the tuff is more than 1800 feet (600 m) thick. Ash fall from the eruption covers an area of at least 4 million square km (about half the size on the continental United States). Ash from the eruption has been recovered from deep-sea cores taken in the Bay of Bengal and in India, roughly 300 miles (500 km) inland (1,900 miles, 3100 km from Toba). Rose and Chesner suggested the ash may have reached central Asia and the Middle East. Ninkovich and others (1978) estimated of the height of the eruption column to be 30 to 50 miles (50 to 80 km) for the Young Toba Tuff. Rose and Chesner, after a study of the shapes of the ash shards, concluded this estimate was too high by a factor of 5 or more.
Tambora - "The Year Without a Summer" 1816 Wikipedia article The Year Without a Summer, also known as the "Poverty Year" and "Eighteen hundred and froze to death" was 1816, in which severe summer climate abnormalities destroyed crops in Northern Europe and the American Northeast. It is now known that the aberrations occured because of the April 5-April 15, 1815 volcanic eruptions of Mount Tambora on the island of Sumbawa in the Dutch East Indies (in today's Indonesia) which ejected over a million and a half tons of dust into the upper atmosphere. As is common following a massive volcanic eruption, temperatures fell on the earth due to reduced sunlight.
Krakatoa and Tambora FAQS from Volcano World by David Elsley
Krakatoa is the modern name of a group of three volcanic islands that exploded violently in 1883, causing an Exodus/ Santorini - like catastrophe throughout southeastern Asia and the western Pacific, and a global year without a summer. Resulting tidal waves were a good deal larger than those of December 26. Ecological catastrophe resulted all over the southwestern Pacific and huge numbers of people and animals who weren't killed immediately died of starvation and disease. The volcano is located in a transtension zone in the strait between Sumatra and Java. A PBS program on Krakatoa showed that the initial problem with Krakatoa was a plug that prevented the escape of magma. Rampino, the volcano expert, figured out that the cause of the most catastrophic explosions was not water seeping into the volcano, which would have made much finer pumice, but the melting of an upper, cooler, level of light colored magma by darker and much hotter magma that followed it in the eruption and mixed with it. This liberated alot of gas, which built up explosive pressure until the volcanic island exploded. A new volcano, Krakatoa Anak, has been building since 1926, growing steadily higher and more violent - though this time nothing was said about a lava plug.
Krakatoa is a stratovolcano, not a caldera volcano. Sometimes called a composite volcano. These volcanos are common, often violent, and typically occur in subduction zones. The thick, viscous magma causes the violence. They emit ash clouds, and pyroclastic flows, as do culdera volcanos. Mount St. Helens and Mount Pinutubo are also stratovolcanos. The eruptions are plinian in character - very high, with pyroclastic flows.
Or rather, it is a type of caldera volcano that resulted from a stratovolcano, depending on your terminology.
Another type of classical cone-shaped volcano is the stratovolcano. However, when it comes to size and the ability to pack a serious punch, stratovolcanoes outclass cinder cones in a big way. In fact, it is quite common to find much smaller cinder cones adorning the flanks of these giant mountain-sized volcanoes. A stratovolcano also has steep sides with a distinguishing cone shape and is frequently composed of several different vents that erupt lava, sometimes in different ways.
Pyroclastic flows, lava domes, and cinder cones sometimes characterize stratovolcanoes. Usually, these types of volcanoes erupt explosively and violently, sometimes completely blowing their tops!
Pyroclastic flows don't really look much like "flowing" eruptions. They look more like big explosions, complete with billowing clouds.What happens during a pyroclastic flow is enormous volumes of extremely hot gases, ash, and rocks rush down the side of a volcano, like an avalanche of sorts.
If the eruptions of a stratovolcano continue long enough to evacuate enough earth from beneath the surface, the entire top of the mountain can completely collapse into the empty chamber below, leaving a caldera. Although a caldera is usually what happens after a stratovolcano blows its top or spills all its guts, there is another extremely powerful type of volcanic eruption that truly qualifies as an Extreme Volcano
Caldera volcanoes are the Extreme Volcanoes. These are the most powerful and catastrophic types of volcanoes in a category by themselves because of the unique way in which they form. This type of volcano is shaped more like an inverse volcano. An enormous magma chamber bulges up beneath the ground from the extremely high pressures of the trapped gases within. Ring-shaped cracks form outward from the magma chamber toward the surface and these act as relief valves for the magma to escape. Once the accumulated pressure has been sufficiently released through a serious of extremely powerful pyroclastic and plinian eruptions, the ground above the magma chamber subsides or caves in, leaving a large depression. Caldera volcanoes are the largest on earth, with some calderas measuring from 15 to 100 kilometers wide.
Scientists are just beginning to understand these types of volcanoes and have only recently identified the characteristics of this type of eruption. Since this type of eruption has not occurred anytime during recorded history there have been no human witnesses to record observations of this type of event. The lack of a real-world example makes it even more difficult for scientists to study this type of volcano and very little about them is understood. But from the evidence that scientists have been able to gather about caldera eruptions in earth's past, all signs point to events so cataclysmic that they may have changed the course of the evolution of life on earth. Witness the following eruptions:
This article discusses the types of caldera-forming volcanos. They are defined as of two sorts - those formed by stratovolcanos, and the bathtub sort such as Yellowstone.
These volcanoes are the deadliest, stickiest, nasttiest, gassiest of the entire lot.
Their eruptions can be earth shaking, cataclysmic- they can have the power of many nuclear explosions. They may bring famine, pestilence, tsunamis, plaques, great pyroclastic flows, darkness for many days or months, global climatic change, and, possibly, very pretty sunsets.
Caldera volcanoes are ones where the diameter of the circular to oval crater exceeds 1 mile. These form when so much lava is erupted (blown out) so rapidly it partially empties the underlying magma chamber. When this happens the summit of the volcanic structure collapses into the emptied magma chamber. Typically the erupted material occurs as airfall or pyroclastic flows.
There have been no recent eruptions from caldera volcanoes- Valley of Ten Thousand Smokes was the last and before it there was Krakatoa (1886) and Tambora (1815)- which caused the year without a summer. Three most famous examples in North America are Yellowstone,Crater Lake, and Long Valley.
Overall at least 138 caldera volcanos, whose crater exceeds 5 miles in diameter, are known. Unlike Crater Lake , many of these have calderas so large and irregular they remained undetected until high-quality aerial or satellite images became available. One of these, LaGarita, located in the San Jauan mountains of southern Colorado is some 20 miles wide and 60 miles long, Yellowstone, with a caldera of 24 by 40 miles is another example. Both these calderas were formed due to the large scale evacuation of a near surface magma chamber (think of the amount of material that has to be blown out to create a hole many miles in diameter and 1,000's of feet deep),and the collapse of the overlying rocks into it.
The eruptions from these caldera volcanoes are largely explosive leading to extensive air fall and pyroclastic flow deposits.
Where they occur:
Island Arcs- Krakatoa, Tambora, Toba, Taupau
Continental Mountains- Crater Lake,
Precambrian Example- Sturgeon Lake- Ontario- a large caldera volcano some 2.7 billion years old
Two kinds of Caldera Volcanoes:
Stratovolcanoes that turn into calderas due to cataclysmic eruptions- Crater lake, Tambora, Krakatoa.
Negative volcanoes- no sign of a volcanic ediface- usually just a large lake or a depression with lots of hot springs- Taupo, Long Valley, Yellowstone, Toba, Sturgeon Lake.
Super Volcano Trigger Found This article discusses how caldera volcanoes erupt. I strongly doubt there is just one cause. According to this article in Discovery News, the dome that forms over the calderas of these volcanoes needs to be flexible for anything to happen. It swells and swells for very long periods of time, until eventually cracks form in the surface. Then the cracks grow, Eventually the cracks get big enough to cause the dome to collapse, triggering the eruption. This article says that unlike smaller volcanos, caldera eruptions are not triggered by smaller eruptions within the volcano. Thie theory predicts that the Yellowstone volcano is a long ways from erupting, because cracks would have formed and be getting bigger if an eruption was imminent.
Pinatubo Volcano: The Sleeping Giant Awakens" (1991 eruption - last erupted four centuries earlier.)
It caused an episode of global cooling.
Iceland is not a place where one thinks of a lot of violent volcanic activity, and it's easy to underrate its volcanos. But it actually has a third of the volcanic activity on the planet, and, sitting on the mid Atlantic ridge, the island was built by extremely violent stratovolcanos and fissure volcanos, that are partially fed by a hot spot under the mid atlantic ridge at that point. Its fissure volcanos are often particularly huge. Laki was such a volcano; it consisted of 10 fissures and extended for ten miles.
In the 1780's, Europe was blanketed by a thick sulfuric haze, people and crops were killed. Following was atleast one bitter cold winter, which killed more Europeans. Benjamin Franklin, living in Paris at the time, wrote about it. The succession of crop failures helped to fuel the French Revolution of 1789. The cause was the explosion of Laki, one of Iceland's volcanos. Iceland is an island today mostly covered with glaciers, between Ireland and Greenland, west of Scandinavia. People continuously battle with its volcanos and take advantage of its volcanic hot springs to bathe in the winter.
Most recently a minor volcanic eruption sent an ash cloud over northwestern Europe in spring of 2010.
Wikipedia article on Laki, the volcano of 1783
Laki Eruptive fissureIt is generally believed that the Laki eruption was derived from magma injected laterally along dikes from a shallow chamber beneath the Grimsvötn caldera, located 40 to 70 km to the northeast beneath the Vatnajökull ice cap.
Wikipedia article on Eyjafjallajökull eruption (Link may not work)
Eyjafjallajökull The stratovolcano, whose vents follow an east-west trend, is composed of basalt to andesite lavas. Most of its historical eruptions have been explosive. However, fissure vents occur on both (mainly the west) sides of the volcano.
Katya volcano Bigger than Eyjafjallajokull, nearby, actually part of the same system, and often erupts with it. Recently unstable.
Both Eyjafjallajokull and Katya are caldera volcanos - which is new news. What is more, a joint eruption of the two volcanos in the 1820's left a thick layer of silicate ash Eyjafjallajokull is a stratovolcano with nearby fissures.
Researchers Puzzle Over How Long Eruption Will Last According to this article, researchers suspect that ice is a factor in the violence of Iceland's volcanos.
Iceland's Eyjafjallajokull volcano, the culprit behind the flight cancellations, has erupted only twice before over the past 1,100 years. The volcano's last active period lasted from 1821 to 1823.
And while the glacier-capped mountain's gently sloping silhouette might suggest a type of volcano more likely to ooze lava than blast ash clouds thousands of feet into the sky, those looks can be deceiving, cautions Benjamin Edwards, a volcanologist at Dickinson College in Carlisle, Pa.
Even volcanoes frequently associated with relatively sedate eruptions can spring surprises, he says.
Typically, volcanoes known for explosive eruptions have magma rich in oxygen and silicates, he explains. And they tend to form conical mountains such as Mt. Fuji in Japan, or Mt. St. Helens, before it erupted in 1980, blasting away the top 1,300 feet of the summit.
Others, with broad, gently sloping sides, such as Hawaii's Mauna Loa, tend to erupt with a thicker, less gas-laden magma that forms fiery fountains in fissures along their flanks, or flows from a main crater.
Yet for such "shield" volcanoes, fresh magma welling up can alter the chemistry of solidified magma from the last eruption, enriching the magma with silicates and oxygen.
One other wildcard is the presence of ice. Meltwater making contact with magma also can trigger an explosive eruption, says Mr. Edwards.
Edward Venzke, with the Global Volcanism Network in Washington, speculates that this is what may have happened in Eyjafjallajokull's case. The network is a collaboration between the US Geological Survey and the Smithsonian Institution's Museum of Natural History.
When the eruption began last month, it did so as a small fissure eruption along a flank of the volcano, he notes. Magma erupted fountain-like, indicating that it contained some gas. But it was more like a typical eruption in Hawaii than Mt. St. Helens.
When that stopped, solidifying magma may have sealed the fissures, allowing pressure to build under the ice-capped summit. As the magma rose, ice melted, providing the water needed to trigger an explosive eruption.
If that's the case, suggests Mr. Venzke, the likelihood that explosive eruptions will continue could shrink with the amount of immediately available meltwater.
But if the explosive nature of the volcano's eruption "is more a function of the composition of the magma, this could go on continuously or episodically for quite a while," he says.
The dust that is such a nuisance to air traffic will provide the information volcanologists need to tell which processes were the most influential in triggering this week's blasts. The clues come not just from the chemical composition of the dust particles, but also in their shapes.
Mt. Redoubt Eruption 2009 - a lot of material on Laki The adjacent Grimsvotn Volcano has a fissure 60 miles long that leads to Laki. Laki is surrounded by a hundred fissures. The fact that Grimsvotn erupted at the same time as Laki and the complexity of the fissures confuses the picture of how long was the fissure eruption called Laki, which was not a continuous fissure but a bunch of smaller ones and cones.
Geologic Setting of Iceland Volcanos
Iceland sits astride the Mid-Atlantic Ridge, a boundary between two tectonic plates, where new crust is being formed by volcanic eruptions as the plates diverge, i.e., they are moving away from each other. Movement on this structure over the last 180 million years or so has separated Europe from North America, and Africa from South America. The island of Iceland is engaged in a geologic race between the spreading motion which is ripping the island apart, and the volcanoes which are building the island up.
Other islands of the Atlantic Ocean created by the volcanism of the Mid-Atlantic Ridge are The Azores, Bermuda, Madeira, The Canary Islands, Ascension, St. Helena, and Tristan da Cunha. But, you probably haven’t heard about any volcanoes erupting in Bermuda because that island group lacks one other geologic phenomenon: the “hot spot.” Iceland also sits above a mantle plume or “hot spot” where magma from deep in the mantle forces its way to the surface. The Hawaiian Islands were formed, and are being formed, by such a hot spot. In Hawaii, the westward movement of the Pacific plate passes over this hot spot and eruptions produce new islands. Iceland, however, is not moving in such a manner.
The 1783 to 1784 eruption at Laki fissure and the adjoining Grímsvötn volcano was the largest single historic eruption of basaltic lava (12 cubic km). Benjamin Franklin, who at the time was serving as ambassador to France remarked on this eruption. The ash cloud caused the “year without summer.” That eruption of basalt lava and clouds of poisonous hydrofluoric acid/sulfur-dioxide compounds killed over 50% of Iceland’s livestock population, leading to famine which killed approximately 25% of the population. It remains to be seen if the current eruption will be as long lasting. So far, the ash cloud from the current eruption has risen to 30,000 feet which affects airline travel, but it has stayed below the stratosphere, so the climate effects are not likely to be as drastic as those in 1783.
Why the Icelandic Volcanic Eruption Could Herald More Disruption
The worst-case scenario in terms of precedent here is the 1783-1784 eruption at Laki (a very large eruption of 14km3 compared to the one in Mount St. Helens in 1980 of 1 km3) that had a huge impact on the northern hemisphere, reducing temperatures by up to 3 degrees. This led to catastrophe far beyond the shores of Iceland (where 25% of population died), with thousands of recorded deaths in Britain due to poisoning and extreme cold, and record low rainfall in North Africa.
By contrast, the eruption of Eyjafjallajökull in 1821-1823 (when only about 0.1km3 was erupted) had little impact beyond the shores of Iceland, where livestock were killed by flourine poisoning. Like 1821-1823, this current eruption is likely to remain small in terms of volume, but in an age of mass aviation, a relatively small amount of erupted ash is having huge consequences.
How much material will be erupted? Observations of surface deformation can throw light on this. These come principally from two sources — the first being a handful of GPS receivers dotted around the volcano by the University of Iceland and the Iceland Met Office, and the second being imaging radar on board satellites.
Differencing of subsequent radar images can give surprisingly accurate maps of the movement of the ground. I and others at Delft University of Technology have been developing algorithms to push the limits of the technique, to extract measurements from radar data in regions where it is more difficult, and with greater accuracy.
The usual pattern with Icelandic eruptions is for rising and stretching of the surface as magma moves up to shallow depths of a few kilometres, followed by contraction and sinking of the surface as magma exits the shallow magma chamber and erupts at the surface.
However, in this case, Delft University working in collaboration with the University of Iceland has detected magma moving upwards until the onset of the initial eruption on March 20th, but very little deformation since then. This implies that the volume of erupted magma is balanced by new magma coming from deep within the crust, perhaps even the crust mantle boundary, and it is impossible to know how much magma may be stored at these depths. Thus, it remains a very real possibility that the volcano will continue to erupt on-and-off for months to come, as occurred during the last eruptive period in 1821-1823.
Measurements of the surface deformation, together with detected earthquakes, have indicated magma rising to shallow depths since the beginning of this year. Questions have been raised why an eruption was not predicted beyond the time scale of a couple of hours prior to initiation.
From analysis of radar data we know of two events at Eyjafjallajökull in 1994 and 1999, that started in a similar way with magma moving to shallow depths (5-6 kilometres). However, in both cases the magma then spread out laterally and remained in the crust. Apparently something differed this time in that stress conditions favoured continued migration of the magma upwards. We have some way to go before we can answer what seems like a simple question, whether magma moving upwards to shallow depths is likely to erupt, or stall within the crust.
At the end of the last ice age, the rate of eruption in Iceland was some 30 times higher than historic rates. This is because the reduction in the ice load reduced the pressure in the mantle, leading to decompression melting there. Since the late 19th Century the ice caps in Iceland have been shrinking yet further, due to changing climate. This will lead to additional magma generation, so we should expect more frequent and/or more voluminous eruptions in the future.
Eyjafjallajökull is a relatively small volcano and unlikely to erupt the volumes of material that will have a significant impact on climate. However, eruptions of Eyjafjallajökull in 1821-1823 and 1612 were followed in short shrift by eruptions of its much larger neighbour, Katla.
Katla thus has shown the potential for large eruptions in the past — the last catastrophic Icelandic eruption prior to Laki was from Katla in 934 when an even greater volume of lava was erupted. If Katla were to erupt in a significant way, the potential for travel chaos and economic damage would thus be much greater than has occurred in the last 24 hours.
Can be found online or rented from Netflix. Geooglical history of Iceland. Iceland is torn by the spreading mid Atlantic ridge from southeast to north. All of Iceland's active volcanos are along the ridge. The ridge spreads at an inch a year. The tearing causes fissure eruptions, which can pour uot huge amounts of lava in a very short time. But Iceland's high volcanoes cannot be explained by the ridge alone as it is the only place along the ridge where theree is a volcanic island. Underlying Iceland is a hotspot, 100 miles wide and 400 miles deep, with its focus under the large glacier. Minerology of the lava in Iceland proves that the hotspot brings up lava from very deep in the earth. 20 million years ago the mid-atlantic ridge drifted across the hot spot and has been locked to it ever since. (I don't know how firmly locked; I saw an aritcle that shows the hotspot moving across Iceland.) New islands still form around Iceland - in 1963 an 18,000 foot coluns of rock and ash shotupin the air and gave birth to a new island off Iceland. Serterian eruption named after it - a very explosive erution caused by interaction of magma with ash.
Vatnajokull is a huge glacier - the largest in Europe. The red cracks are fissures - the pink area roughly corresponds to the mid oceanic ridge.
Here are two maps of Iceland's hot spot; one shows the rifts as well.
A long ice age was born 1.5 million years ago when chagnes in earth's tilt and orbit cooled th eplanet. (?) (think Himalays and jioning of North and South America also played a role.)
Laki, the volcano of 1783, was a massive fissure eruption 16 miles long, consisting of a line of 10 fissures. It was one of the greatest eruptions in recent history. It caused a drop of 2 - 3 degrees F in the Northern hemisphere for several years. It started on June 8, 1783, and over 8 months a chain of new eruptions occurred, spreading the fissure, and the volcano erupted continuously for over 8 months. It erupted large amounts of sulfur dioxide into the environment, which manifsted as thick red fog. It was seen over Iceland in June, over London and Paris within weeks, and by July (only weeks later), it had sperad across the entire northern hemisphere. The fog consisted of sulphur dioxide confined with water to make a sulphuric acid haze, which blocked out the sun. Three bitter winters followed in the northern hemisphere, with spring floods, and famine. All of the northern hemisphere froze over. Changes were caused to climate of the rest of the planet; India had terrible drought, and Japan had famine.
I also found mention of an ancient oceanic microplate foundered beneath central Iceland - probably caught by the core of magma.
Currently the Iceland glaciers are melting at a rate matched only at the end of the last ice age, when volcanic activity increased because of decompression caused by the melting of the ice. 5% of Iceland's ice cap has melted in the last 40 years. Valleys once filled with ice are now free of it.
An article suggests that Laki's hot spot does not come from the Earth's mantle, but rather from a process that dates to the original opening of the Atlantic Ocean, and caused basalt flood volcanos to develop over what is now East Greenland and England, during the early Tertiary - between 62 and 47 million years ago. The flood basalts may be what caused Eurasia and North America to divide; it and hotspot activity are common at the beginning of continental rifting. There was more flood basalt activity in Ethiopia in the mid Tertiary. In Continental Flood Deposits, by J.D. Macdugall (Google books), Carlson and Hart suggest that such basalt flood activity in the Clolumbia and Oregon Plateaus and the Snake River Plain, 18 to 11 million years ago, gave rise to the Yellowstone hotspot. But the hot spot was on the borders of Idaho, Nevada and Utah at the time, making it unlikely that, for instance, it gave rise to the flood basalt volcanism. More likely the flood basalt volcanism derived from the melting of rock behind the Cascade subduction zone.
Here is a map of Laki's fissures and lava.
This information was found on a blog whose url I couldn't decipher.
According to Wikipedia, Laki is on the Grimsvotn system. Grimsvotn is under the Vatnajokull glacier near the hotspot. It is the most active volcano in Iceland, and was considered by Icelanders to be a gateway to hell. According to the article, Laki itself did not erupt in 183, but fissures opened up on each sdie of it. Grmsvotn erupted at the same time (and kept erupting for two more years). Laki immediately killed a fifth to a quarter of Iceland's population (both by poisoning and by famine), and 50% of Iceland's livestock, caused a drop in global temperatures and the year without a summer, famine throughout Europe and eastern North America, and drought in India; estimated to have killed six million people globally. In England people died from dramatic symptoms of hydrofluoric acid and sulfuric acid gas poisoning. This did have to do with a prevailing high pressure system and with wind directions.What should be a concern, it appears, however, is that this particular volcano, although in itself not that large, is often a precursor to the eruption of the Katla volcano, which is nearby but further north- east. While the current eruption started away from a glacier, the Katla lies under the Myrdalsjoekull glacier, and the precedents are not good.
"Eyjafjallajokull has blown three times in the past thousand years," Dr McGarvie told The Times, "in 920AD, in 1612 and between 1821 and 1823. Each time it set off Katla." The likelihood of Katla blowing could become clear "in a few weeks or a few months", he said.
Iceland's Laki volcano erupted in 1783, freeing gases that turned into smog. The smog floated across the Jet Stream, changing weather patterns. Many died from gas poisoning in the British Isles. Crop production fell in western Europe. Famine spread. Some even linked the eruption, which helped fuel famine, to the French Revolution. Painters in the 18th century illustrated fiery sunsets in their works.
The winter of 1784 was also one of the longest and coldest on record in North America. New England reported a record stretch of below-zero temperatures and New Jersey reported record snow accumulation. The Mississippi River also reportedly froze in New Orleans.
The last eruption of Katla was not that
severe, although there was severe flooding. But it can be violent, throwing
large volumes of material into the air. The consequence of the Laki eruption of
1783-4 (it lasted for eight months and ejected over 9 cubic miles of
basaltic lava and a quarter of the population of Iceland died from
starvation, the effect on winter temperatures in the US was evident.
But it is not the fine particles that apparently cause the most climate impact,
rather the large
volumes of gases that also are ejected and turn into acid aerosols that
contribute to the disastrous
consequences. It has been projected that there were some 8 million tons of
fluorine and 120
million tons of sulphur dioxide released. To put this in context, during the
Mount Pinatubo eruption (which also had a short term cooling on global climate)
the volcano is projected to have emitted some 20 million tons of
sulfur dioxide and that this lowered the global temperature by perhaps 0.8
deg C in 1992. (The aerosols reflecting back more solar energy into space.)
In January, 2013, PBS Nova presented "Doomsday Volcanos", which argues that three of Iceland's deadliest volcanos, Katla, Laki and Hekla, or atleast two of the above, are likely to erupt soon. This is quite a contrast to the arguments above that none of them appear immediately likely to do very much! Data by Sigrun Hreinsdottir at the University of Iceland was presented, based on monitors on the Katla volcano, showing that that caldera has risen 4 centimeters over several years. She has a web site, on that monitoring. This web site has changed in the past two days since I spoke with her. It previously showed annual seasonal fluctuation of about 4 cm, alternating between the caldera bulging upward and bulging north and east, with a net rise of 2 cm over three years. Now it more consistently shows bulging upward and north and east over time, though seasonal fluctuation is also evident. There are also several statements in "Doomsday Volcanoes" that "Katla is rumbling". From what I can learn, there clusters of small earthquakes (magnitude 3 and 4) 2011 that had the government concerned enough to prepare to evacuate people, but the volcano quieted down. This documentary must have taken atleast the intervening time to prepare. The other reasons for worry are that Eyja recently erupted (which lead to a massive drop in deformation on more than half of the monitors), and that Katla usually erupts every 50 years and has not erupted in 100 years, though of course it depends on how one defines an eruption. Flooding from under the glacier, always caused by Katla erupting, has occurred several times since 2010. Evidently all of these volcanos erupt mildly far more often than they "erupt". Dr. Hreinsdottir told me in an e-mail on January 7, 2013, that they really don't know if Katla is likely to do a major eruption any time soon, or a very small one.
One other thing; for atleast 500 years, though Katla has erupted on the average every 50 years, it has never erupted during the winter. (Before that it is not known if Katla ever erupted during the winter, but it is thought to probably not happen very often.) The weight of the glacier varies with the season and affects its ability to expand and therefore to erupt. This is clear on Dr. Hreinsdottir's graphs of its expansion by month for the past three years. So it is very unlikely that it will erupt within three months of the January 2013 showing of "Doomsday Volcanoes". By spring, everyone will have forgotten all about it. ;)
Thor Thordarson, who is more worried about Katla, presented evidence that 3000 years ago, an eruption of Hekla smothered Europe with ash, to a far greater extent than Eyjafjallajokull, which is now called Eyja. Allegedly, in 934 AD, an eruption from Katla caused double the damge of that - and it seems like there'd be a historical record of it if it had, since people lived on Iceland at the time. Either eruption should have dwarfed the Laki eruption of the 1780's, and frozen the continent for years, the latter in the middle of the medieval warming period. Hekla is evidently on a cycle. On Nova this was described as alternation between mild eruptions and violent ones, with an especially violent eruption beginning the new phase with perhaps a half hour of warning. Vague "signs" were referred to that the mild cyle is ending. Online I'm finding just slightly less vague discussions of a very specific three-phase cycle by Hekla, and evidently it is possible to tell by the characteristics of eruptions when a phase ends.
"Doomsday Volcanoes" referred to an eruption of Katla in 934 AD, that was twice the size of the catastrophic Hekla eruption of 3000 BC. The discussion then focused on the imminent odds of this occurring. But this turns out to have been a very unusual eruption of Katla. It was specifically the opening of the Eldgja fissure, and the last time such a fissure eruption occurred in the same location was around 5500 BC. Current concern about what Katla is going to do concentrates on the caldera itself - which erupts on a significant scale on the average every 50 years -, not on the Eldgja fissure. I didn't even see where "Doomsday Volcanoes" presents any results of monitoring of Eldgjya.
This map makes little sense of any concern that Katya would cause havoc through an eruption of Eldgja, by making it look like the two volcanoes are not related. However, Sigrun Hreinsdottir sent me two articles with better graphics.
The 75 km long Eldgja fissure actually runs from the southeastern edge of the Katla Caldera, under the glacier, for I guess 15 km, before it emerges to run for 60 km "subaerially" - in the open, almost to the larger glacier where the hotspot is. The zone of ash fall covered 60 km in both directions, and its center included the Myrdalsjokull glacier. The fissure eruption probably melted the snow over it and erupted into the air, just as Katla does. This would have made it possible to know at the time that it was an eruption of Katla. In addition to the gas fallout related above, the eruption completely transformed the terrain of southeastern Iceland; changing the coastline, burying rivers and creating new ones.
This is not a typical eruption of Katla, and I haven't found any reason to expect a repeat of it soon. A similar eruption in the same location happened in 5050 BC.
Larsen, Gudron. Holocene eruptions within the Katla volcanic system, south Iceland: Characteristics and environmental impact. Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik. JOKULL No. 49. (2000)
Larsen, Gudrun. Katla: Tephrochronology and Eruption History. Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, IS-101,Reykvavik, Iceland (firstname.lastname@example.org) Developments in Quaternary Sciences Vol 13. (2010).
A discussion of the 1000 BC Hekla 3 eruption is at Wikipedia. The eruption caused an 18 year span of climate worsening that is recorded in the Irish oak bogs, in Greeland ice cores, and in the bristletone pine seuence. An alternative dating of 1159 BC would make it a cause of the Bronze Age collapse, but in any case it would have occurred during the dark age that followed. In 1000 BC new states and cultures had barely begun to emerge. A Slice Through Time, Dendrochronology and Precision Dating, M.G. L. Baillie, Google Books, argues that Santorini accounts for an event in 1627 BC, something started in 1159 BC, which Hammer argued is Hekla 3 in Iceland. Hammer argues that the Iceland date calibrates to 3000 to 3400 BC at 1-sigma, 2900 - 3600 BC at 2 sigma. There appears to be disagreement on whether the climate event of 1000 to 1159 occurred in 1000 or in 1159, rather than two different events that occurred at those dates.
I found one discussion that dates eruptions of Hekla and Eyja in terms of the settlement of iceland. "The previous eruption of Eyjafjallajokull in 920 AD, just after Iceland was settled, was not followed by an eruption near Katla until 934 AD even if Katla had erupted ahead of Eyjafjallajokull in 920." This suggests that eruptions happened and people who were there at the time recorded it. This article tears apart with historic evidence the notion that Katla is likely to erupt if Eyja recently erupted. Actually Katla has often erupted when Eyja, which erupts much less frequently, had not erupted. The two volcanoes are considered probably linked by an underground vent or fissure system, and seismic activity indicates interaction between them.
The earthquakes may represent "intrusion events" which term is poorly defined, but probably has to do with lava movements underground along a "fissure" system between two volcanoes. As of March, 2010, recent earthquake activity had clustered in three areas; shallw quakes around and within the Eyja caldera, shallow quakes in the easter part of Katla caldera, and quakes with a deeper focus in the Goadabunga area between the first two clusters. One possible interpretation is that a cryptodome - an underground lava dome - is active beneath the area. "The presence of viscous rhyolitic lava beneath Katla and Keyja makes for potentially explosive eruptive activity, if an eruption occurs." (The Volcanism blog, 3/4/2010) Intrusion events do not always lead to eruptions. They occurred in 1994, 1999, and 2009, and those times, things calmed down. On the other hand, an April 2011 article refers to small shallow earthquakes 20 km WSW of Laki, belonging to the Katla volcano. This article refers to a "dike intrusion" elsewhere in Iceland getting to the surface in 1878 and opening a 25 km long volcanic fissure (in NE Iceland). On "Doomsday volcanoes" this definition of a "dike intrusion" was the definition of a "fissure".
Here is a chronology of Icleandic eruptions during the tenth century.
Year ~920. Somwhere on the Reykjanes ridge. Location is unknown. But a ash layer is known from this eruption.
Year ~920. Katla volcano eruption. Ash layer named Katla-R.
Year ~934. Katla volcano creates Eldgjá volcano fissure. Lava flow from Eldgjá volcano fissure flows over Álftaver, Meðalland and Landbrot. Mýrdalssandur is sad to have been created in this eruption by a big flood from Mýrdalsjökuli following this eruption.
The same chronology raises the possibility that little is made of the 934 eruption because Iceland can't go 50 years, often not 20, without a major volcanic eruption.
It probably was some eruption, according to a Wikipedia article on Eldgja fissure.
According to Wikipedia, "Eldgjá is a volcanic canyon in Iceland. Eldgjá and the Katla volcano are part of the same volcanic system in the south of the country. Eldgjá means "fire canyon" in Icelandic.
"Situated between Landmannalaugar and Kirkjubæjarklaustur, Eldgjá is the largest volcanic canyon in the world, 270 m deep and 600 m wide at its greatest. It was discovered by Þorvaldur Thoroddsen in 1893. The first documented eruption in 934 was the largest flood basalt in historic time. The areal extent of the lava is around 800 km2. An estimated 18 km3 of magma poured out of the earth."
Eldgja and Laki fissures run parallel to each other - but they are not on the same volcanic system. Eldgja is part of Katya (or vice versa) and Laki is part of Grimsvotn under the bigger glacier - though it does not erupt nearly as often as Grimvotn does.
It was explained on "Doomsday Volcanoes", that the volcanoes of southeastern Iceland are often connected by underground fissures that serve as conduits for lava. They connect volcanoes to each other and can cause such volcanoes as Eyja and Katla to be connected to each other. If they contact the surface the result is a fissure volcano.
I thought fissure / flood basalt volcanoes resulted from the rift in the earth's crust at that location. The plates are pulling apart at this location. However if Hawaii's volcanoes are really fissure volcanoes, they may have a different mechanism.
A discussion of the Eldgja Fissure System argues that the Eldgja eruption in 935 AD lasted 3 - 8 years and produced 19.6 cubic km of lava, making it the largest basaltic flood eruption in historic times. An estimated 219 Mt of SO2 was released into the atmosphere, which may have produced 450 Mt of H2SO4 aerosol. However the environmental impacts probably didn't exceed those of Laki and Tambora - which were catastrophic enough. The cold and rain and the sulphuric acid fallout caused massive deaths throughout western and central Europe, the latter both from starvation and from poisoning and lung damage.
It turns out that many of Iceland's larger volcanoes are actually fissure volcanoes with mountains or calderas in the middle where most of the eruption usually occurs, but they are capable of erupting along the entire fissure. This makes sense because the volcanoes are being created by rifting that is pulling the crust apart. Even Hekla is really a fissure volcano, though I know of the entire fissure erupting just once.
The most frequent volcano to erupt in Iceland is Grimsvotn. It is beneath the nrothwestern side of the great glacier, and must be near the hot spot. It erupts every ten years. It is surmounted by lakes on the glacier, and its eruptions often cause huge floods from glacier mount. Laki is on the same system as Grimsvotn, and Grimsvotn erupted when Laki did and kept erupting for two more years. An eruption in 2011 caused high plumes, and resulted incancellation of 900 flights in Iceland, the UK, Greenland, Germany, Ireland and Norway on 22 to 25 May. Until 25 May the eruption scale was larger than the 2010 eruption of Eyja.
Even though it may never happen again, no discussion of catastrophic volcanoes would be complete without mentioning the explosion of Thera/ Santorini in 1680-1520 BCE.
The eruption of Santorini in Greece in 1,650 B.C. was one of the largest (VEI=6) in the last 10,000 years. About 7 cubic miles (30 cubic km) of rhyodacite magma was erupted. The plinian column during the initial phase of the eruption was about 23 miles (36 km) high. The removal of such a large volume of magma caused the volcano to collapse, producing a c aldera. Ash fell over a large area in the eastern Mediterranean and Turkey. The eruption probably caused the end of the Minoan civilization.
Time was 1680-1520. Most likely around 1645-1580. Possibly as early as the end of the Hyksos period, accounting for vague things written about that period. Before end of reign of Tuthmosis III of Egypt. In temple workrooms from Tuthmosis I to III, pumice used that came from this volcano. During reign of Tuthmosis III or the regency of his mother, the Mycenean conquest of Crete occurred. This is demonstrated by a changeover in where what Egytian artifacts are found in relation to what on Crete, and the styles Cretans wear in Egyptian art, temple paintings and that sort of thing. Thera is believed to have exploded about 50 years before Minoan Crete finally fell.
The explosion of Thera/ Santorini destroyed the island of Santorini, which was a main base of trade and possibly the most important center of Minoan civilization. There was ecological devastation and tidal wave devastation on Crete. Minoan civilization was badly weakened and fell to the Myceneans within two generations.
The volcano and the collapse of parts of the culdera, created huge tidal waves around the Mediterranean region, ash fall, darkness, possibly for days, corrupted water, strange animal behavior, animal deaths, disease, and disrupted the weather for years (according to Chinese records from the time). This may be the source of the story of the ten plagues of Egypt, and could also pertain to the story of the drowning of Pharoah's army in the sea. A volcano of that size in that location would also have looked and acted much like the cloud by day and column of fire by night supposed to have led Israelites out of Egypt. Egypt held Palestine from the end of Hyksos rule through the 18th and 19th dynasties, and Pharaoh's armies were stationed all along the coast of Palestine. The 18th dynasty began with chasing the Palestinian and Syrian Hyksos out of Egypt across the Sinai into Palestine. The 19th dynasty ended with Israel in existence, and suffering defeat at the hands of Egypt, and the Philistine invasions. In between, Hapiru and desert bedouins who worshipped Yahweh, led resistance against Egypt from the hills.
As is usually the case with catastrophic volcanoes, Santorini is part of a volcanic island arc behind a subduction fault where several plates are sliding together.
The Eruption of Thera: Devastation in the Mediterranean
Devastation of Crete
The Minoan Eruption
BBC: History: The Fall of Minoan Civilization about the work and theories of Floyd McCoy
Nisyros, a similar volcanic caldera, near Santorini This site has a discussion of the plate tectonics that cause the arc of volcanoes, with a map.
The plate major plate boundary that runs through New Zealand twists over on itself between the north and south islands. This contributes to very violent tectonics in the area. The southern part of one of the main islands is expected to fall into the sea one of these days. New Zealand is so tectonically unstable that they find it unsafe to have a proper modern airport. Instead they have a small, primitive airport in the hills.
There was actually a great quake at a point on the fault between New Zealand and Antarctica several days before the Dec. 26 quake in the Indian Ocean.
Three Tectonic Plates Collide Down Under
New Zealand Tectonics
Breaking up with Gondwanaland. Marine magnatic anomalies on Australia's western margin reveal the true story. Christian Heine. U Of Sidney, Inst of Marine Science.
Taupo Volcano This lake on the North Island in New Zealand was created by the largest volcano in the past 5,000 years - which supposedly no people were immediately around to witness. It created a lake the size of Singapore, and devastated a region the size of the state of New York. It occurred around 130 AD.
Yellowstone's Super Sisters: Taupo, New Zealand
Tectonic Map of western United States
Laramide or Thin-Skinned Tectonics in the Northern Rocky Mountains (this and succeeding two pages)
Geomorphology from Space. See Chapter 2: Tectonic landforms. Includes the southwestern US, southern California, the Cascades, New Mexico, and the Rockies.
This might or might not happen and might or might not inundate some or all of the U.S. In "Megaquake", Discovery channel, April 10, 2005, there was discussion of the fact that successive quakes and water action have cracked the entire side of an elongated volcano on one of the Canary Islands, and that successive quakes and volcanism is likely to cause the side of the mountain to collapse into teh ocean. This mountain has regular collapses of this sort but it might collapse in one piece or piecemeal. If it collapsed in one piece it would generate a monster tsunami that would reach the eastern Atlantic coast. This must have happened repeatedly over time and I've not seen the historical evidence of such catastrophe along the eastern Atlantic Coast. It is unclear whether a tsunami would affect the Carolinas, central America, or every city on the east coast of the U.S.
Another tsunami threat on the east coast is that the coastal shelf off of the Carolinas is unstable.
Scientists Warn Of Massive Tidal Wave From Canary Island Volcano By Steve Connor Science Editor The Independent - London 8-29-1
BBC Science News: Tidal Wave Threat may be over-hyped
Both the end Permian and end Cretaceous events are controversial. The end Permian event was just before the rise of the dinosaurs; it ended teh paleozoic era, and the next stage was the Triassic era of the Mesozoic. There is controversy about whether a monster volcanic eruption or a meterorite impact caused it, and good evidence that both events, which would have occurred during the same period of time, contributed. The earth actually was not exactly geologically nor meteorogically stable throughout the entire Triassic period. The end-Cretaceous or K-T event marks the end of the Mesozoic and the end of the dinosaurs - well, all except modern birds. There is also controversy about whether this was caused by a meteorite impact or an extremely large volcanic eruption, again with good evidence that both probably contributed. The end of the Cretaceous in 65 million BCE was followed by the Cenozoic; the "new age".
The Day the Earth Nearly Died transcript
An alternative theory of the Permian extinction:
Becker's Australia: Impact Deja Vu? A Look Inside the Crater part 1 and Becker's Australia: Impact Deja Vu? A Look Inside the Crater part 2
EXTRATERRESTRIAL CHROMIUM IN THE PERMIAN-TRIASSIC BOUNDARY AT GRAPHITE PEAK, ANTARCTICA. A. Shukolyukov1, G.W. Lugmair1,2, L. Becker3, C. Macisaac1, R. Poreda4. 1Scripps Insti-tution of Oceanography, University of California. Lunar and Planetary Science XXXV (2004)
Earth Science: A Possible End-Permian Impact Crater from Science Week
Disaster down-under: Australian impact craters
Scientific American article not available online; Luann Becker, Repeated Blows, Scientific American, March 2002, 78-83
Science article; Chrondritic Meteor fragments associated with the Permian-triassic boundary in Antarctica Science, 302: 21 November 2003, 1388 - 1392
Fullerenes and Interplanetary dust at the Permian-Triassic boundary Robert J. Poreda and Luann Becker. Astrobiology, 3: Nov 1, 2000.
Deccan Traps Basalt flood eruption in India around 65 million years ago may have helped wipe out the dinosaurs.
The End Cretaceous (K-T) Extinction
Catastrophism and Mass Extinctions Page of links to discussions on causes of the end-cretaceous extinction
BBC Science and Nature: Crater of Death
Wikipedia article: Cretaceous-Tertiary extinction event
This page by Dora Smith
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