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Volcanoes of the World

Volcanism occurs... at the plate margins... at divergent boundaries, as the sea floor spreads, e.g., the spreading submarine ridges and rises; and at the subducted margins of convergent plate boundaries... when the oceanic edge of one plate collides against the oceanic edge of another plate, so forming an island arc, e.g., the Sunda Arc, the Philippines, or when the oceanic edge of one plate collides against the continental edge of another plate, e.g., the Cascade Range volcanism. at the hot-spots or mantle-plumes, as the Hawaii- Emperor chain, Iceland, Azores, Yellowstone etc., and as the flood basalts or Large Igneous Provinces, e.g., CRB, Deccan, Parana, Siberian Traps etc.

Sea floor spread by intermittant volcanism at the mid-ocean ridge (top left) results in the recording by subsequent lavas of the geo- magnetic polarity reversals (left bottom) and the resulting marine magnetic anomalies can be mapped by the magnetometers towed by ships (bottom right).

Map showing the Mid-Atlantic Ridge splitting Iceland and separating the North American and Eurasian Plates. The map also shows Reykjavik, the capital of Iceland, the Thingvellir area, and the locations of some of Iceland's active volcanoes (red triangles), including Krafla.

The Mid-Atlantic Ridge, which splits nearly the entire Atlantic Ocean north to south, is probably the best- known and most- studied example of a divergent-plate boundary.

Lava fountains (5­ p;10 m high) spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano.

View of the first high- temperature vent (380 °C) ever seen by scientists during a dive of the deep- sea submersible Alvin on the East Pacific Rise (latitude 21° north) in Such geothermal vents--called smokers because they resemble chimneys--spew dark, mineral-rich, fluids heated by contact with the newly formed, still-hot oceanic crust. This photograph shows a black smoker, but smokers can also be white, grey, or clear depending on the material being ejected.

The deep-sea hot-spring environment supports abundant and bizarre sea life, including tube worms, crabs, giant clams. This hot-spring "neighborhood" is at 13° N along the East Pacific Rise.

Plate boundaries can be either active, i.e., divergent versus or convergent, or passive (transform)

either by the convergence of oceanic edges of plates Volcanism occurs at the subducted margins that form... or by the convergence of continental edge of one plate and the oceanic edge of the other.

A convergent plate boundary, e.g., the convergence of Nazca and South American plates

Juan de Fuca ridge and the associated plates and plate boundaries off the Pacific North- east and Canada. Note that the Cascadia subduction zone is also called the “Filled Trench”, as this trench got filled by sediments carried by the huge runoff from land that has characterized this region particularly since the Last Ice Age.

Nintyeast Ridge

The Hawaii-Emperor seamounts have evolved over the past ~65 Ma as the Pacific plate traversed a fixed mantle plume. (

Archaea Habitats: Rotorua, New Zealand

For information on the LIPs on the internet, try Also visit the USGS volcanoe sites, starting with and the links provided there.

Photograph by Lazlo Keszthelyi Deccan traps, the ~10 6 km 3 flood basalt province in peninsular India, extruded at or about the K/T boundary.

Mt. Pinatubo: June 13, 1991 El Chichon, March

Satellites tracked the spread of airborne sulfuric acid mist formed by SO 2 from the 1991 eruption of Mt. Pinatubo, Phillippines 7/4-7/10/91 (after circulating the earth) 5/20-6/6/91 (before eruption)

The two volcanoes had remarkably similar build-up

El Chicon Mt. Pinatubo

Aerosol loading before and after Mt. Pinatubo's eruption. Note the simultaneous increase in tropospheric and stratospheric loading.

Tropopause folds seasonally purge lower sratospheric material into the troposhpere.

The ratio between (separation of) ruby and CO 2 backscatter coefficients indicates the median size of sulfuric acid aerosol particles.

But their decay phases were notably different El Chicon Mt. Pinatubo

El Chicon Mt. Pinatubo

Conclusion Multi-year, multi-wavelength lidar studies of two major volcanic events reveal details of buildup and decay that are important for proper climatic modeling of such events. Over the United States, build-up from these two tropical volcanoes appears to be similar but decay is dissimilar. Simultaeously, both the troposphere and the stratosphere are affected by such eruptions, a heretofore unknown result.

Pinatubo eruption, June 15, This image was collected during the beginning of the 3-hour- long climactic eruption. The yellow X is the approximate location of the vent and the red outline is the coastline of the northern Philippines. (R. Holasek)

Ice contact and Subglacial Volcanism

The worldwide distribution of sub-glacial volcanic deposits Iceland Alaska, British Columbia, Yukon and the Cascades Antarctica Andes Hawaii

Catastrophe at Lake Nyos, Cameroon On August 21, 1986, a massive cloud of CO 2 gas from the lake flowed out over nearby towns and claimed 1,700 lives. The victims were not poisoned, the simply suffocated: being denser than air, CO 2 would tend to settle near the ground and be rather slow to disperse. Lake Nyos, Cameroon