sign in sign up
<<
Home , Cascade Volcanoes

Volcanoes of theUnited States fountain, Kilauea, Hawaii, 1960 Yolcanoes of the by Robert L. Smith and Roy A. Bailey Volcanic activity has played a dominant role in shaping the face of the Earth. Much of the natural beauty of the land, its mineral wealth, and the fertility of the soil is owed to volcanism, especially in the Western States. At one time or another during the last 70 million years, volcanic rocks covered nearly all of the Western States of Wash- ington, , , Nevada, Arizona, Utah, !daho, and large parts of Montana, , Colorado, New Mexico, and Texas. Still older volcanic rocks, now largely deformed and metamorphosed, are found in nearly every State.

2 (:;:i::\t'isr WN\\

r:.N

Summit and pit craters, Mauna Loa, (photo by United Sfafes Air Force) ln a general way, the older the rocks the Active Volcanoes less well preserved are the features that allow us to interpret their origin. Thus, for Active volcanism in the United States is best understanding of volcanoes and confined to the Hawaiian Islands, the Aleutian volcanic rocks, one must study the youngest lslands, the Alaska Peninsula, and the examples. ln the Western United States, Cascade Mountains. where much volcanism has occurred within The Hawaiian lslands consist entirely of the past few million years, there are abundant volcanic rocks that form giant shield examples of well-preserved volcanic volcanoes; one rises nearly 30,000 feet available for study. Some outstanding from the ocean floor. By far the dominant examples can be found in the Cascade rock type is dark gray to black in Mountains in , Oregon, and the form of lava flows, cinders, , ash, , where a few volcanoes and bombs. may still be active; the On the island of Hawaii are Mauna Loa, Plateau in Oregon and Washington; the the largest in the world, and Kilauea, Snake River Plains in ldaho; Yellowstone one of the most active. During an eruption Park area in Montana and Wyoming; San at Kilauea in 1959-60, great fountains of Francisco Peaks and Sunset Crater area lava, some as high as 1,900 feet, were in Arizona; the Jemez Mountains, N. Mex. ; observed near the volcano summit. Lava Mono Craters and Lake County, from the fountains ran into an old pit crater Calif.; and many other areas in Nevada, and filled it to a depth of 365 feet, forming Utah, Colorado, and western Texas. a lava lake. Late in 1963, nearly 4 years

4 quakes volcano, and after the eruptions, the crust on top of the within and below the lake was nearly 50 feet thick and the tiltmeters measure the contraction and temperature of the lava below the crust was expansion of the top of the volcano relative stilt about 2,0OOo Fahrenheit (1,100' to moving lava inside. Still other instruments and thermocouples-are used Celsius). -pyrometers Kilauea is of specia! interest to to measure temperatures of erupting lava to learn because the erupted material comes from fountains and lava flows. ln order great depth and provides clues to the more about the internal constitution and geochemical constitution of the Earth. lt formation of the Earth, chemists determine the and is also a particularly good site for geochemi- the chemical composition of petrologists mineralogists cal studies because of its frequent but gases, and and frorn the relatively mild eruPtions. study the minerals that crystallize The U.S. Geological Survey maintains the lavas. the Hawaiian Volcano Observatory on the The Aleutian lsland Arc, including summit of Kilauea in Hawaii Volcanoes Alaska Peninsula, is more than 2,000 miles active National Park, which is visited by more long and contains about 36 historically them than 500,000 persons each year- At the and many extinct volcanoes. Among but Observatory, a team of geologists, geo- are some of the world's most beautiful physicists, and geochemists studies every little-studied volcanoes. The composite aspect of volcanic activity. Seismographs volcanoes Pavlof, Shishaldin, and Pavlof constantly record the tremors and earth- tSister are examples. Bogoslof lsland is a

Shishaldin Volcano, Aleutian lslands hs :"1\ ryM rc

Novarupta Dome and surrounding pumice cone, Katmai National Monument, Alaska disappearing volcano, having emerged and composite cones of Mounts Baker, Rainier, submerged in the sea more than once in St. Helens, Adams, Hood, Mazama, and historic time. Most of the Aleutian lavas Shasta. These High Cascade volcanoes are consist of black to gray rocks called built primarily of rocks called andesifes, and . which are intermediate in chemical composi- Of the several active volcanoes on the tion between basalts and . Andesitic Alaska Peninsula, Mount Katmai (Katmai volcanoes are usually great cones of rubble National Monument) is the most notable. In consisting of interlayered lava flows and 1912, one of the most remarkable eruptions of fragmental deposits called mud flows. historic time occurred near its base. About These form when eruptions take place 2 cubic miles of ash and pumice erupted through crater lakes, when fragmental lavas in the form of incandescent ash flows or and enter streams, or when water avalanches. The "river of sand," as the early from melting snow or rain saturates and exptorers called it, flowed more than 15 miles mobilizes previously erupted deposits. down a great glacial , filling it to a Volcanic mud flows may be hot or cold depth of more than 400 feet. This valley and may deposit boulders weighing many is known as the "Valley of Ten Thousand tons. Very young mud flow deposits are Smokes" because of the thousands of common on the flanks of and (gas vents) that formed on the other Cascade cones. surface of the volcanic deposits and gave ln some areas of the world, mud flows have off steam and other vapors for many years. been the major cause of destruction and ln the Cascade Mountains of Washington, loss of life during volcanic catastrophes. Oregon, and California are the well-known Such an eruption in 1919 from Kelud Volcano I ffiEXPLANATION Rhyolite, osh ond pumice Ir- (welded tuff) F- :l Docite, ondesile

Bqsolt {. Ia -I l---t| - - Tcrtiory sediments i l-J- -\l E Prc-Teriiory rocks \ Cross-section of Valles caldera, Jemez Mountains, New Mexico, showing the domed caldera floor and ring of rhYolite lava domes.

11 10 in Java covered over 50 square miles of dormant. , the southernmost land with mud and Iava blocks. More than volcano of the Cascade chain, was recently 5,000 lives were lost and 100 villages active with small eruptions in 1914-15. completely or partly damaged. This great Lassen Peak is famous among volcanoes devastation was caused by the ejection of because it is one of the largest known over 1 billion cubic feet of water from plug domes. A plug dome is a part of a Kelud's . volcano formed by the vertical rise of a is the volcano that lost great sticky mass of lava which remains most of its top about 7,000 years ago during standing above the crater rim. Commonly a tremendous . Nearly 12 great vertical grooves are formed in the cubic miles of ash and pumice erupted, margin of as the material oozes producing under the volcano a void so Iarge from the orifice. The mechanism may be that the top caved in to form a great hole compared to the squeezing of toothpaste 6 miles across. Depressions formed in the from a tube. Subsequent eruptions from top of volcanoes in this manner are known plug domes are among the most dangerous as . They differ from craters that known. Gases dissolved in the lava may are produced by explosion rather than by burst forth violently, shatter the dome, and collapse. The caldera of Mount Mazama is cause the formation of extremely mobile now filled with water to a depth of over avalanches of hot blocks, rock dust, and 1,700 feet and is known as Crater Lake. gas. Such avalanches may travel at speeds Although most of the Cascade cones up to 100 miles an hour and devastate seem to be inactive, some are probably only everything in their paths. lt was an eruption

W { "lT. " W{ffi *ffi.,

Mazama ash shards x 300 Crater Lake, Oregon lphr tto by Washington National Guard)

12 13 of this type in 1902 from Mount Pel6e in the miles in area. When deposited, these great West lndies which destroyed the nearby sheets of ash were so hot that the particles town of St. Pierre and killed nearly 30,000 fused together to form rocks known as people. welded tufts. Recent geologic studies have revealed that welded tuffs are perhaps the most abundant rhyolitic rocks in the Western Ancient Volcanoes United States. Tens of thousands of cubic miles are known in Nevada alone, and great There are several areas in the United volumes are also recognized in the San Juan States where, for many thousands of years, Mountains of Colorado, southwestern New the only activity has been that of hot springs Mexico, the Big Bend region of Texas, and and so/fataras (steam vents). Yellowstone southeastern Arizona. National Park is the most famous of these ln the Jemez Mountains in New Mexico, areas. lt is visited each year by thousands about 1 million years ago, eruptions similar of people who come to see the geysers, to those at Yellowstone produced nearly mud pots, boiling hot springs, steam vents, 50 cubic miles of welded tuffs. Removal of and beautiful carbonate and silica deposits this large volume of material from the formed by precipitation from the hot waters. abyssal storage chamber caused a great Such phenomena are vestiges of a former circular block of the Earth's crust (more period of very active volcanism and are than 10 miles in diameter) to subside several commonly considered to represent the thousand feet, producing a giant caldera at waning stages of volcanism. We cannot be the surface. Formation of this, the Valles sure, however, that some day more violent Caldera, was similar to that of Crater Lake, volcanic activity may not begin again. but of special interest to geologists is the The youngest and most dominant volcanic subsequent, more complex history of the eruptions in Yellowstone Park produced I Valles Caldera. Renewed pressure from lavas called rhyolite'. Chemically, rhyolite is betow uplifted and arched the subsided high in silica and is the volcanic equivalent circular block so that its center rose even of granite. Among active volcanoes rhyolite t; higher than its original elevation. During is exceedingly rare. ln the geologic past, and after this uplift, new eruptions of however, rhyolitic eruptions were more rhyolitic lava broke out along the fracture common and among the most spectacular system around the uplifted circular block of natural phenomena. Over 600 cubic and built a ring of 15 new volcanoes. Valles Caldera miles of rhyolite erupted f rom the Yellowstone Detailed studies of the volcanoes alone during their last active have allowed geologists to relate this periods. Two-thirds of this amount erupted rhyolitic volcanism to more deeply seated as ash flows like the "river of sand" that processes of granite formation. Volcanism caused the "Ten Thousand Smokes" in of this type is now known to have occurred Alaska in 1912. The remaining 200 cubic in many other areas of the United States. miles of material issued as great sticky The San Juan Mountains of Colorado are an lava flows. outstanding example, as are the Mono So great was the volume of the flows of Craters in California. They, like Little GIass ash and pumice that valleys were completely and Big Glass Mountains in northeastern filled and the intervening ridges were California, are famous for black volcanic covered. The ash flows merged to form glass (obsidian) and for the large blocks flat-topped plateaus thousands of square of pumice that have recently become so

14 15 ,'ffiun# W

Layered basalt flows of the Columbia River Plateau, Hell's Canyon, Oregon-ldaho border popular as ornamental stones. The Mono Columbia River Plateau has an area of Craters include some of the world's finest 100,000 square miles, and the total volume examples of rhyolitic pumice cones and lava of basaltic lava approximates 35,000 cubic domes. Their forms range from simple, almost miles. lndividual lava flows can be traced perfectly symmetrical cones of pumice and for distances of more than 100 miles. Such ash, to cones whose craters are partly or lavas must have been almost as fluid as completely filled or overflowing with lava. water to have covered such large areas so Some cones are completely covered with uniformly. lava flows that have piled up to form steep- On the northern edge of the Snake River sided lava domes. Those cones containing Plains is the Craters of the Moon National lava that did not overflow the crater rim are Monument. Here, basaltic lavas erupted similar to the plug dome of Lassen Peak but perhaps less than 2,000 years ago. The vents are much smaller and formed by more from which the lavas issued are localized on fluid lavas. + great fissures and show a wide variety of Recurrently, throughout geologic time, forms, ranging from cinder cones built very fluid basaltic lava has erupted from entirely of very frothy red and black lava swarms of fissures to form vast lava cinders, to spaffe r cones formed by the piling plateaus. The Columbia River Plateau of up of liquid lava blobs and droplets around Washington and Oregon and the Snake River the vent. Both aa and pahoehoe lavas are Plains of ldaho are among the finest found at "Craters of the Moon." Pahoehoe examples of this type of volcanism. The and aa are Hawaiian terms adopted the world

16 17 over for two principal types of basaltic of andesitic and similar lavas. Fine examples Iavas. Pahoehoe is very fluid lava with a of the clustered types are the volcanic fields smooth to ropy surface and the flows may of the San Francisco Mountains, Ariz., travel long distances. Aa is more viscous and Mount Taylor, N. Mex. lava that forms steep-sided flows seemingly Hundreds of other localities for volcanoes composed only of craggy blocks, but usually and volcanic rocks are known, and this very containing a continuous fluid interior. brief discussion simply serves to emphasize Occasionally the surface and sides of that the United States, particularly the West, these basaltic lava flows solidify to form a has been one of the most volcanically thick outer crust. Yet the hot lava inside active areas in the world in recent geologic continues its forward movement and time. Because we do not yet know the real. eventually drains out of its own crust to causes of volcanism, we cannot say whether form lava tunnels or lava tubes. Water eruptions will recur in areas like New entering such tunnels may freeze in the Mexico, Arizona, or Nevada. We can be winter and, because of the excellent sure, however, that in our lifetime volcanoes insulation provided by the basalt crust, in Hawaii and Alaska wil! erupt again. may not thaw in the summer even under desert conditions. Excellent examples of these ice caves and lava tunnels may be seen in the Modoc Lava Beds National Monument, Calif. Basaltic lava fields and cinder cones are numerous in many parts of the West. Some of these are isolated volcanic vents, but basaltic vents are commonly clustered near or around large volcanoes composed

i-: fsN

-*s

Columnar jointing in basalt flow, Devil's Post Pile trF-ftt National Monument, California (photo by National .' #,'*i'l Park Service)

This publication is one of a series of general interest publications prepared by the U.S. Geological Survey to provide rnformation about the earth sciences, natural resources, and the environment. To obtain a catalog of additional titles in the series "Popular Publications of the U.S. Geological Survey," write: Branch oI Distribution or Branch of Distribution U.S. Geological Survey U.S. Geological Survey 1200 South Eads Street Box 25286, Federal Center Arlington, VA 22202 Denver, CO 80225 Pahoehoe in Hawaii

18 For sale by the Superintendent of Documents, U.S. Government Printing Offrce lVashington, D.C. 20402

rt U.S. GOVERNMENT PRINTING OFFICE: 1980- 341-618-5 As the Nation's principal conservation agency, the Department of the lnterior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American lndian reservation communities and for people who live in lsland Territories under U.S. administration.

ru