Volcanism: Creating the Earth's Surface Goals 1. describe the types of volcanic cones 2. identify the recent volcanic centers of the western United States 3. review the volcanic provinces of the world Introduction For a significant number of people, their most direct and important connection with geology is through volcanoes. Nearly 80% of all the population around the Pacific Rim live near volcanoes. For these people, the possibility of a volcanic eruption poses a direct threat to their lives. Eruptions also affect people far removed from the volcano. The eruption of Mount Tamboro in 1815 in Indonesia affected the climate worldwide. It was responsible, in part, for the last famine to occur in western Europe. More recently, the eruption of Mount Pinatubo in the Philippines affected global climate by introducing a large amount of S02 into the atmosphere. Volcanoes and their eruption also strongly impact airline travel, agricultural production, and air and water quality. Geologically, volcanoes are important because they have been responsible for the creation of the hydrosphere and the atmosphere. These were formed by the release of gases from the Earth's interior by eruptions. In addition, volcanoes and volcanic activity are important for the formation of certain types of mineral deposits. Volcanic Provinces of the World In general, volcanism is not uniformly distributed around the world. The interiors of North and South America, central Asia, and Antarctica all lack recent volcanism. Volcanism is concentrated in narrow belts at the margins of continents. This association reflects the direct connection between plate tectonics and volcanic activity. Specifically, most active volcanoes are associated with plate boundaries where crust is created or destroyed. Thus, volcanoes are found along mid-ocean ridge systems or subduction zones. Whereas the majority of active volcanoes have a direct link to the creation of crust by plate tectonic processes, some, like Hawaii, are located in the interiors of lithospheric plates. These volcanoes are believed to be associated with hot spots located beneath the plates in the mantle. Thus, most current volcanic activity present ly occurring can be readily explained by current geologic theories. Yet, if one examines the geologic record, there are large volcanic provinces whose connection with plate activity is not evident. For example, the Deccan Traps of India is a large basaltic plateau that lacks a clear connection to older plate boundaries. Yet this volcanic province produced large amounts of volcanic material. Numerous similar examples of such volcanic activity are evident in the geologic record. Clearly, a complete understanding the evolution of the Earth requires understanding the origin of this type of volcanism. Although explaining the origins of these provinces is difficult, knowledge of their geographic location and size provides a sense of the dynamic nature of the Earth's surface and the processes occurring in its interior. Volcanoes of the Continental United States In the last 5 million years, the western part of the United States has been the site of extensive and varied volcanic activity. Volcanism has occurred from the Rocky Mountains to the Pacific coast, a distance of 1800 km, and from the Canadian to Mexican borders. Although volcanism on such a scale occurs at other places on the Earth, the variety of volcanic landforms produced and the types of volcanic material erupted are unusual. The volcanoes vary from the large composite cones of the Cascades to small cinder cones in the southeast. In addition, the materials erupted vary from basalt to rhyolite. Interestingly, most of this volcanic activity is not directly associated with present plate boundaries. The volcanoes in the Cascades are associated with subduction of the Juan de Fuca plate beneath North America, but this subduction lacks any accompanying seismic activity. Until the concept of plate tectonics and the understanding of the tectonic evolution of western North America in the mid-1970s, the origin of this volcanism was not clear. Today it is believed to have originated in large part due to subduction along the western margin of North America. Because media attention focuses primarily on the large composite volcanoes of the Cascades, the general public is generally unaware of the volcanic character of the western United States.

Volcanism: Creating the Earth's Surface

Name: Lab Section: Date:

Activity 1: Volcanic Provinces of the World Read the following descriptions of different volcanic provinces around the world. Locate the areas described on the world map (Fig. 8-1). Enter the name of each volcanic province on the appropriate blank in Table 8-1. South Sandwich Islands . Also known as the Scotia arc. The volcanoes form an isolated chain in the South Atlantic. There are 12 subaerial volcanoes with elevations mostly below 1000 m. However, they rise several thousands of meters from the sea floor. Because of their remote location, the volcanoes are only poorly known. Aleutian Arc. Curved chain of recent volcanic islands stretching from Alaska to Russia. The chain contains 80 major volcanoes with numerous smaller ones. The largest are in the eastern part of the arc. Shishaldin is a 3000 m high volcano and one of the most active in the arc. Deccan Traps. Large volcanic province in western India erupted in the Eocene. Estimated volume of 106 km2. The original extent of the basalts is estimated at 500,000 km2. Iceland. Sits astride the Mid-Atlantic ridge. The island covers 50,000 km2 and is made almost exclusively of basalt. Aeolian Arc. This volcanic chain is located in the Mediterranean north of Sicily. It consists of seven major islands, all of which are made up exclusively of volcanic material. Volcanism along the chain has occurred over the last 500,000 years. The famous volcanoes Stromboli and Vulcano are part of this group. Andes. Volcanoes stretch along nearly the entire western coast of South America. The chain consists of a northern zone (Columbia-Ecuador), central zone (southern Peru-northern Chile) and a southern zone (southern Chile). Within these zones are some 500 major volcanic structures. Volcanic activity has spanned the last 23 my. The largest volcanoes are classic composite cones and can reach elevations of 6000 m. Hawaiian Islands. Linear chain of volcanic islands in the Pacific. Subaerial volcanoes extend for 500 km. The largest and most active islands occur at the eastern end of the chain. Tahiti. Two volcanic islands 35 km apart in the Pacific. Volcanoes have a maximum elevation of 2200 m and rise nearly 4000 m from the ocean floor. Lavas are mostly basalt. Indonesian Volcanoes. These volcanoes stretch nearly 6000 km in a slightly curved east west trending chain. The largest historic eruption (Tambora, 1815) and the fourth largest (Krakatau, 1883) have occurred in this volcanic region. More than 500 young volcanoes have been identified. In historic times, 78 volcanoes in the arc have erupted and 50 exhibit geothermal activity. Kuriles. Chain of volcanic islands stretching from Kamchatka Peninsula to Japan. There are sixteen major islands each with several volcanoes. The chain includes a total of 250 Quaternary volcanoes (160 subaerial and 89 submarine). Individual volcanoes are up to 3000 m and very active. Japan. Japan forms the intersection three volcanic arcs. The northeast chain (Northeast Honshu) is a continuation of the Kuriles volcanic chain. The southwestern chain consists of the Southwest Honshu and Ryukyu arcs. The southern chain consists of the Izu-Bonin chain of volcanic islands. These continue north from the Mariana Islands. Nearly 440 volcanic centers have been identified in this area (105 of the Quaternary volcanoes on Earth). Of these, 140 are considered active.

Mariana Islands. The Mariana Islands are a N-S trending group of young volcanoes. The volcanic chain consists of 12 islands and a much larger number of seamounts. The tallest island is Agrigan at 882 m. The islands and seamounts are spaced from 50 km to 70 km apart. Taupo Volcanic Zone, New Zealand. Nearly 16,000 km2 of exposure of mostly rhyolite. It is on a linear trend with the Tonga-Kermadec Islands. Mexican Volcanic Belt. A 1000 km long belt of volcanoes up to 100 km wide that trends E-W across Mexico. The active zone consists of 10 major volcanoes. The tallest-Popocatepetl (5450 m) and Pico de Orizaba (5675 m}-are classic composite volcanoes. Thousands of smaller volcanoes that were active for short periods of time also occur in the belt. Lavas are mostly basalts and dacites. Karroo Basalts. 25,000 km2 of basalt exposure in southern Africa. Original extent is estimated to be 2,000,000 km2. Individual basalt flows up to 10m thick. The Karroo are of Jurassic age. Galapagos. Group of volcanic islands 1000 km west of South America. The islands form a group 400 km in diameter. They occur on a submarine platform that lies in 1500 m of water. The lavas are basaltic and form major shield volcanoes. One of the most volcanically active regions on Earth. Azores. Ten volcanic islands trending eastward from the Mid-Atlantic Ridge. They are located on a submarine ridge 700 km long and 2000 m below sea level. The islands are mainly Holocene in age. Canaries. Seven volcanic islands arranged in an E-W trend and 400 km long. They are located off the east coast of Africa. The largest island is Tenerife and covers 2000 km2. A large caldera 15 km wide and 2000 m above sea level contains two active volcanoes. Aegean Arc. A volcanic group of islands in the Aegean sea. It extends from Greece south. The arc is about 500 km long and only 20 km wide. It contains about seven islands. Santorini has had historic eruptions prior to 1950 and Nisyros has strong geothermal activity. Historic vo lcanism has not occurred on the other islands of the group. Islands of Gulf of Guinea/Cameroon Line. A line of volcanic islands 700 km long that continues onto the continent. The volcanoes on the continent have been very deadly. Ascension. Located on the Mid-Atlantic Ridge at 80S. The island covers 100 km2 with a maximum elevation of 860 m. It has erupted mostly olivine basalt. St. Helena. Situated 800 km east of the Mid-Atlantic Ridge. The island covers 120 km2 and has a maximum elevation of 800 m. However, it rises from the ocean floor nearly 4000-4500 m. Estimated volume of 400 km of mostly basalt that was erupted in the Pliocene. Trinidade . A volcanic island 1140 km east of Brazil (20° 30'S, 29° 20'E). The island rises 5000 m from the sea floor and covers 6 km2 with elevations up to 600 m. The lavas are late Pleistocene to Holocene. East of the is land is a series of seamounts. Tristan de Cunha. The largest of a group of three volcanic islands forming a group 50 km in diameter. Tristan de Cunha rises 3000 m from the sea floor with a maximum elevation of 2000 m. Last erupted in 1961. Papua New Guinea-New Britain. A group of over 100 Cenozoic volcanoes trending roughly east-west. Of the volcanoes, 14 are considered active and approximately 10 have erupted in the last 100,000 years. An eruption of Mount Lamington in 1951 killed 3000 people.

Tonga-Kermadec. These two volcanic chains are an oceanic extension of the volcanoes on New Zealand. Tonga consists of nine active volcanoes that form six permanent islands. Kermadec contains another three volcanic centers. Although the islands themselves are small, the volcanoes rise several thousand meters from the sea floor. Because of their isolation, these volcanoes have been visited by few volcanologists. Lesser Antilles. Volcanic island chain along the eastern margin of the Caribbean sea. The islands have been very active and 30,000 people have been killed by volcanic activity this century. The latest activity has been on Montserrat. In 1902, the eruption of Mount Pelee on Martinique resulted in considerable loss of life. Reunion Island. Located in the Indian Ocean about 125 km east of Madagascar. The island is 18.3 km by 6.5 km and formed of olivine basalt lava flows. The is land has a central ridge running down its axis with its highest point at 396 m. The lavas were erupted from fissures. Easter Island. Easter Island (Rapa Nui) is a small volcanic island 3700 km west of Chile and 500 km east of the East Pacific Rise. The island covers 100 km2 with a maximum length of 24 km. The highest point on the island is only 511 m above sea level. The island was formed by eruptions from three volcanic centers. All centers have been extensively eroded and there have been no historic eruptions. The oldest lavas are 3 million years old. The surface of the island is formed of lava flows erupted from numerous scoria cones. Cape Verde Islands. This group of fifteen islands lies 600 km west of Senegal. They form a chain of volcanoes generated as the African plate moved east over a hot spot in the South Atlantic. The youngest island is Fogo, at the western end of the chain. It consists of a single volcano with a diameter of 25 km and is topped by a caldera 10 km across. The caldera occurs in the northeast comer of the island. Eruptions last occurred in 1950 and 1995. From 1500 to 1760, the volcano was in nearly continuous eruption. Kamchatka arc. This continental arc forms part of the Pacific ring of fire. It contains, at least 100 major volcanic structures. Of these, about fifteen have been active in historic times. The arc forms the continuation onto the continent of the Kurile island arc. Kliuchevskoi is a classic stratocone with an elevation of 4,750 m. Parana Flood Basalts. Large basaltic volcanic field covering nearly a million square kilometers. Mostly located in Brazil. The original extent of the basalts is estimated at 2,000,000 km2. Mostly of Cretaceous age.

Activity 2: Volcanoes of the Continental United States

Read the following descriptions of different volcanic provinces in the western United States. Locate the areas described on the map of the United States (Fig. 8-2). Enter the name of each volcanic province on the appropriate blank in Table 8-1.

Cascades. Holocene volcanism extending from Washington state to northern California. The composite volcanoes are associated with subduction, although the volcanoes appear to be only 40 km above the subducting plate. Except for the existence of the volcanic arc, there are none of the other geologic characteristics of subduction. Although the spectacular composite cones are most visible, they commonly rest on a basalt shield. In addition, other volcanic edifices occur between and to the east of the main volcanic cone. Baker. Northern most of the U.S. Cascade volcanoes, this volcano is 3285 m high. It was active in the mid-1800s. Mount St. Helens. This has been one of the most active of the Cascade volcanoes. It is also the youngest. The oldest rocks are only 40,000-50,000 years old and the pre-1980 symmetric cone had been built in only 2000 years. Six debris flows off the volcano have traveled over 100 km and reached the Columbia River. Adams. This volcano is located 50 km east of Mount St. Helens. It is 3742 m high and covered by dozens of glaciers. The main cone has an erupted volume of200 km3 making it the second largest in the Cascades. It has not erupted in historic times. Most of the volcanic cone was built in the last 20,000 years.

Hood. Located 75 km east-southeast of Portland, Oregon, Hood is the highest peak in Oregon. The volcano is 3426 m high. In the last 15,000 years, four eruptions have produced lahars and debris flows that have moved along several rivervalleys. Because these valleys are now developed, similar events in the future could have tragic consequences. Newberry Caldera. Located in central Oregon some 60 km east of the Cascade range, Newberry is one of the largest of the young volcanoes found in the United States. It is a shield volcano formed in the last one-half million years. Newberry covers an area of nearly 1600 km2 and has an estimated erupted volume of 450 km3. Three Sisters. Group of three volcanic peaks-North Sister (3075 m), Middle Sister (3063 m), and South Sister (3158 m)- located in central Oregon. These volcanoes were constructed mostly in the Late Pleistocene and have not been the site of historic volcanic activity. Crater Lake. One of the most beautiful volcanoes, Crater Lake lies in southern Oregon. Crater Lake is the caldera (8 km x 10 km) formed by the eruption of Mount Mazama. Before the caldera-forming event, this ancestral volcano had an elevation between 3300 m and 3700 m. The eruption happened 6,845 years ago and produced a layer of volcanic ash that blanketed much of the western United States. This unit is an important geologic time marker. Wizard Island is a small volcanic island formed soon after the caldera formation. Shasta. Located in northern California, Shasta is the largest of the Cascade composite cones. Its erupted volume has been estimated at 350 km3. The summit occurs at 4317 m and is nearly 3500 m above the surrounding countryside. A large subsidiary cone, Shastina, on the west flank has a summit elevation of 3758 m. Lassen. The southernmost of the Cascade volcanoes, Lassen was formed in the last 600,000 years. Lassen consists of a stratocone, a dacite dome field, and small shield volcanoes. It last erupted in 1915-1917. Medicine Lake. Lying 50 km east of the Cascade volcanoes, this shield volcano has an estimated volume of 600 km3

and occurs in northern California. It is larger than the largest Cascade volcano. The volcano is young (1 my) and has erupted basalt and rhyo lite. It is topped by a caldera 7 km x 13 km. Simcoe. This volcanic field lies to the east of Adams and is only poorly known. It consists of lava flows erupted in the last 5 million years. The field contains at least 36 cinder cones. Indian Heaven. Exposed between Adams and St. Helens, this volcanic center is marked by a 30 km long string of overlapping cinder cones and shield volcanoes. The largest peaks have elevations between 1500 m and 1800 m. The entire field covers about 600 km2. Lava tubes are common in the older large lava flows. Snake River Plain-Yellowstone. A 80-km wide band of basaltic and rhyolite volcanism occurs in southeastern Idaho. It extends 450 km to the Yellowstone region in northwest Wyoming. The volcanic rocks become younger to the east. Rhyolitc material was erupted prior to 5 my ago, but the province has been the site of basaltic eruptions since. Snake River Plain. The Snake River Plain forms a 600 km long arc of volcanic rocks that is 65 km to 100 km wide and stretches across southern Idaho. The plain is comprised of basalt and rhyolite flows. With time, volcanism has moved from east to west: Kings Bowl. This is a small (2.6 km2) volcanic field lying near Craters of the Moon. The field contains lava flows, spatter cones and explosion craters. Kings Bowl itself is a crater 85 m x 30 m and 30 m deep. The field is slightly over 2000 years old. Yellowstone. Located at the eastern end of the Snake River Plain, Yellowstone represents the most recent eruptive activity of this volcanic plain. Since 2.5 my ago, Yellowstone has erupted 6000 km3 of volcanic material. The region contains three large calderas each associated with large pyroclastic deposits. Eruptive material includes basalt and rhyolite. This region is the site of intensive geothermal activity.

Craters of the Moon. Lying along the northern edge of the Snake River Plain, Craters of the Moon is a basaltic volcanic field formed in the last 15,000 years. The most recent eruption occurred 2000 years ago. The volcanic field contains 25 cinder cones and 8 fissures and fissure systems, and it covers 1600 km2. Colorado Plateau. The Colorado Plateau is an uplifted area near the Four Comers region. Volcanism in the four comers states occurs around the margin of this tectonic province. On the north, the volcanism consists of small monogenetic volcanic fields. On the south and west sides, large mafic volcanic fields with silicic centers of volcanic activity are more common. Mount Taylor. This volcanic center is slightly northwest of the center of New Mexico. It consists of a composite volcano and a volcanic cone. The volcano, Mount Taylor, has a basal diameter of 20 km and a summit elevation of 3445 m. It is formed mostly of pyroclastic material. The accompanying volcanic field has many explosion craters and domes and covers an area 30 km x 60 km. San Francisco Peak. The basalt and rhyolite volcanic rocks of this volcanic field were erupted in the last 6 my. The youngest activity occurred approximately 10,000 years. The volcanic field covers 5000 km2 with an erupted volume of 500 km3. Nearly 600 individual volcanic vents have been identified. Springerville. Another of the marginal Colorado Plateau volcanic fields, Springerville is located southeast of San Francisco Peak and is about half the size of this larger field. The field contains nearly 380 vents and lava flows. Volcanic activity occurred from 2.5 to 0.3 my ago. Most of the vents are small cinder cones. Rio Grande Rift-Jemez Zone. In New Mexico, recent volcanic activity has occurred along two intersecting linear zones. The Jemez zone is a nearly 600 km long and trends northeast-southwest. Volcanism began 13 my ago and is as recent as 1000 years. It is the site of basaltic and rhyolitic volcanism. The Rio Grande Rift is marked by small, isolated volcanic centers. It trends north- northeast and stretches from Colorado to Mexico. The intersection of the two zones is marked by the largest volcanic centers in New Mexico. Zuni-Bandera. Part of the Jemez zone, the Zuni-Bandera lava field covers an area 90 km long and from 1 km to 35 km across. The field is a combination of pyroclastic material and lavas that are mostly basalt in nature. Lava flows have composite thicknesses of 20 m to 60 m and were erupted from 74 vents. The field occurs near the Arizona-New Mexico border. Jemez. This volcanic center is an ash-flow volcanic complex. Activity has spanned the last 14 my and produced nearly 2000 km3 of volcanic material. It lies between the Taos and Taylor volcanic fields. The most prominent land feature of the volcanic field is the Valles caldera formed about a million years ago. The caldera is 22 km in diameter. The Bandelier Tuff is a pyroclastic unit erupted about 1.45 my ago. Taos. This is the largest volcanic field along the Rio Grande rift and occurs on the New Mexico-Colorado border. It covers about 7000 km2 and erupted material varies from basalt to rhyolite. There are at least 35 monogenetic shield volcanoes in the field. Basalt was erupted in the center of the field and rhyolite near the margins. Raton-Clayton. This volcanic field is located in northeast New Mexico. It is composed mostly of cinder cones that were formed in the last million years. Individual cones often have an associated lava flow. Eastern California. The other concentration of recent volcanic activity in the western United States occurs in eastern California. These are generally monogenetic volcanic fields that have erupted mostly basalt. Mono Craters. This is a 12 km arc of domes and explosion craters. These were formed in the last 350,000 years. The youngest lavas may be only 200 years old. The erupted material is mostly siliceous.

Inyo Craters. This is a chain of silicic domes and lava flows in eastern California located west of Mono Craters. The total volume of erupted material is only 0.8 km3 and was erupted in the last 6000 years. Long Valley. Long Valley is a caldera 17 km x 32 km that is very young. About 0.7 my ago, a large eruption produced the caldera and vented the 500 km3 Bishop Tuff, a large pyroclastic unit. A series of earthquakes with intensities of 6 in 1980 suggests magma may still lie under the caldera. Inyo and Mono Craters are on the margin of Long Valley. Coso. The Coso volcanic field is a monogenetic volcanic field situated south of Long Valley. It was formed during two periods of volcanic activity. One occurred 4 my to 2.5 my ago and the other from 1 my to 0.04 my. The volcanic field is a geothermal area. A commercial geothermal operation was begun here in 1987.