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North and South Menan Buttes are two of the world's largest tuff cones. Their volumes are 0.16 cubic miles (0.70 cubic km) and 0.07 cubic miles (0.30 cubic km), respectively. Diamond Head. a better known tuff cone, has a volume of 0.15 cubic miles (0.6 cubic km). Photo by Mike Lovas, NASA-Ames, 1969. Figure 5-67 in Greeley, 1977.
The deposits that make the cones are fairly uniform and without structures or with thin beds. The tuff is lapilli-size particles made of volcanic glass that has been altered by the addition of water. Photo by Steve Mattox, 1988.
Some layers preserve bomb sags, indentations made by larger pyroclasts that landed on the soft layers of tuff. Photo by Steve Mattox, 1988.
Vertical aerial view of the Menan Buttes. The crater of North Menan Butte is about 3,000 feet (900 m) in diameter and the cone is about 6,000 feet (1,800 m) in diameter. U.S. Department of Agriculture photographs CXS-6AA-50 and 51, July 1960. Figure 5-66 from in Greeley, 1977.
Cross-section of North Menan Butte. From Hamilton and Myers (1963).
View towards North Menan Butte. The cones rise about 800 feet (250 m) above the surrounding plain. Photo by Steve Mattox, 1988.
Sources of Information:
Creighton, D.N., 1987, Menan Buttes, southeastern Idaho, in Beus, S.S., ed., Centennial Field Guide Volume 2 Rocky Mountain Section of the Geological Society of America, p. 109-111.
Greeley, R., 1977, 5. Aerial guide to the geology of the central and eastern Snake River Plain, in Greeley, R., and King, J.S., eds., Volcanism of the eastern Snake River Plain, Idaho: A comparative planetary geology guidebook: NASA, Washington, D.C., p. 59-112.
Hackett, W.R., and Morgan, L.A., 1988, Explosive basaltic and rhyolitic volcanism of the eastern Snake River Plain, in Link, P.K., and Hackett, W.R., eds., Guidebook to the Geology of Central and Southern Idaho: Idaho Geological Survey Bulletin 27, p. 283-301.
Hamilton, W., and Myers, W.B., 1963, Menan Buttes, cones of glassy basalt tuff in the Snake River Plain, Idaho: U.S. Geological Survey Professional paper 450E, p. E114-E118.
Stearns, H.T., Crandall, L., and Steward, W.G., 1938, Geology and ground-water resources of the Snake River Plain in Southeastern Idaho: U.S. Geological Survey Water-Supply Paper 774, 268 p.
Well, that depends on how big the eruption is and how big the debris is that you are concerned about. As you might imagine a big eruption will send material farther. Additionally, the big material from any eruption doesn't get thrown as far as the finer stuff.
Volcanologists go out into the field to figure out the distribution of erupted pyroclastic material. They will go to numerous sites around the volcano and measure (in general) 3 things: 1) the total thickness of the pyroclastic deposit at each location; 2) the average size of the 10 largest pumice at each location; and 3) the average of the 10 largest lithic clasts at each location (a lithic is a pre-existing rock that is blown apart in the explosive eruption). They then draw contours around the data that they have collected. In some cases, if the geologists are studying a very old eruption, they may not even know where the vent was. The contours of the thickness and size measurements should close around the vent so that its location can be determined.
Left: This photo shows a pumice deposit from a 1980 pyroclastic flow at Mount St. Helens. Note person holding pumice boulder. Photo courtesy of U.S. Geological Survey.