America's Volcanic Past
|"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994|
|[NOTE: This list is just a sample of various Alaska features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Alaska.]|
|Aniakchak National Monument|
The Aniakchak Caldera, covering some 10 square miles, is one of the great dry calderas in the world. Located in the volcanically active Aleutian Mountains, the Aniakchak last erupted in 1911. The crater includes lava flows, cinder cones, and explosion pits, as well as Surprise Lake, source of the Aniakchak River, which cascades through a 1,500-foot gash in the crater wall. The site contains the Aniakchak Wild River.
|Bering Land Bridge National Preserve|
Bering Land Bridge National Preserve:4
The Preserve was established in part to preserve significant volcanic features which are rare in the Arctic. The Preserve contains extensive lava flows and ash/steam explosion craters now turned to lakes called maars. Maar lakes were formed when magma rose to meet ground water and permafrost ice, causing massive steam explosions. There are four maar lakes in the Preserve, which are the largest craters of their type on the planet. Their explosions have occurred over a time span of more than 100,000 years. The most recent happened 17,500 years ago and buried the ice-age landscape with thick layers of volcanic ash.
Devil Mountain Lake:4
Devil Mountain Lake, an unusual double crater maar lake is the largest maar lake on the planet.
Lost Jim Lava Flow:4
Located in the eastern part of the Preserve are a variety of volcanic features. The Lost Jim Lava Flow and associated cinder cones were formed less than 2,000 years ago. This rugged lava flow covers more than 100,000 acres and provides an opportunity to watch vegetation recapture land that has been totally devastated.
|Denali National Park and Preserve|
Denali National Park:9
The oldest terrane and rocks in the park are found near the park entrance, and are called the Yukon-Tanana rocks. These are shallow sediments with volcanic flows and intrusions (molten injections of rock) that formed in a very young Alaska, about 400 million years ago. These rocks have been buried very deep for a long time, and subjected to heat and pressure that changes the rocks into metamorphic kinds (schists, gneiss, phyllites).
Mount McKinley, the highest mountain in North America at 20,320 feet, is at the heart of Denali National Park and Preserve. Towering 18,000 feet above the neighboring lowlands, the mountain, otherwise known as Denali, an Athabaskan Indian name meaning the "The High One", rivals the vertical relief of the world’s greatest mountains. Mount McKinley is possibly the highest granitic pluton in the world, which is undergoing continual tectonic uplift. The majority of the rest of the mountains and rocks in the park are sedimentary, a testament to the millions of years that central Alaska was an open seaway. Mount McKinley is still growing at about 1 millimeter per year. In the process of plate tectonics, (the Pacific plate is diving beneath Alaska, or the North American Plate) land surfaces in Alaska are continually compressed and folded, which pushes up Mount McKinley, as well as the rest of the mountains in the Alaska Range. Mount McKinley is primarily made of granite, which is very hard and resists weathering much better than its sedimentary (shale, limestone and sandstone) neighbors. As Denali is pushed up, it remains, like a resistant sentinel, above the others, which wear down faster through the eons of freezing, thawing, and glaciers grinding and scraping. At 56 million years old, Denali rock is also much younger than most of its sedimentary neighbors, which varies from 100 to 400 or more million years old.
During the birth of Mount McKinley 56 million years ago when molten magma solidified deep beneath central Alaska, volcanic activity (eruptions at the surface) was also occurring in the park, and produced red, yellow and brown basalts, rhyolites, and other volcanic rocks. These rocks can be seen along the park road, particularly at Polychrome Pass, named for the colorful volcanic rocks exposed there. Things again heated up at Denali about 38 million years ago, when another period of volcanic activity resulted in the basalts and andesites found exposed at Mount Galen, and along the park road at the west end of Eielson Bluffs.
Similar to Mount McKinley, another granitic blob crytallized at depth beneath the surface to become Mount Foraker, the second tallest peak in the park at 5,303 meters (17,400 feet).
|Katmai National Park and Preserve|
Katmai National Park and Preserve:5
The 15 active volcanoes that line the Shelikof Strait make Katmai National Park and Preserve one of the world's most active volcano centers today. These Aleutian Range volcanoes are pipelines into the fiery cauldron that underlies Alaska's southern coast and extends down both Pacific Ocean shores (the so-called Pacific "Ring of Fire"). This Ring of Fire boasts more than four times more volcanic eruptions above sea level than any other region in historic times.
Novarupta and the Valley of Ten Thousand Smokes:5
The June 1912 eruption of Novarupta Volcano altered the Katmai area dramatically. Severe earthquakes rocked the area for a week before Novarupta exploded with cataclysmic force. Enormous quantities of hot, glowing pumice and ash were ejected from Novarupta and nearby fissures. This material flowed over the terrain, destroying all life in its path. Trees up slope were snapped off and carbonized by the blasts of hot wind and gas. For several days ash, pumice, and gas were ejected and a haze darkened the sky over most of the Northern Hemisphere. When it was over, more than 40 square miles of lush green land lay buried beneath volcanic deposits as much as 700 feet deep. At nearby Kodiak, for two days a person could not see a lantern held at arm's length. Acid rain caused clothes to disintegrate on clotheslines in distant Vancouver, Canada. The eruption was ten times more forceful than the 1980 eruption of Mount St. Helens. In the valleys of Knife Creek and the Ukak River, innumerable small holes and cracks developed in the volcanic ash deposits, permitting gas and steam from the heated groundwater to escape. It was an apparently unnamed valley when the 20th century's most dramatic volcanic episode took place. Robert Griggs, exploring the volcano's aftermath for the National Geographic Society in 1916, stared awestruck off Katmai Pass across the valley's roaring landscape riddled by thousands of steam vents. The Valley of Ten Thousand Smokes, Griggs named it.
The nearly circular Novarupta Dome that formed during the 1912 eruption of Katmai Volcano, Alaska, measures 800 feet across and 200 feet high. The internal structure of this dome -- defined by layering of lava fanning upward and outward from the center -- indicates that it grew largely by expansion from within.
|Lake Clark National Park and Preserve|
Iliamna and Redoubt:7
Two active volcanoes, Iliamna and Redoubt, form an important link in the Pacific "Ring of Fire". Venting steam, snow-capped, and rising more than 3,050 meters (10,000 feet), each is an impressive volcano to be viewed from the eastern side of the park.
Within the park the mountains of the Alaska and the Aleutian Ranges join. The Chigmits, an awesome, jagged array of mountains, are the result of centuries of uplifting, intrusion, earthquakes, volcanism, and glacial action.
|Wrangell-St. Elias National Park and Preserve|
The Wrangell Mountains, which form much of Wrangell-St. Elias National Park and Preserve, are made up largely of thousands of lava flows that have been erupted mostly from broad volcanoes during the past 26 million years. This extensive volcanic terrain, which is called the Wrangell volcanic field, covers about 4,000 square miles - an area a little smaller than the State of Connecticut - and extends eastward from the Copper River Basin through the Wrangell Mountains, into the St. Elias Mountains of Alaska and the Yukon Territory of Canada. All the volcanoes of the western Wrangell Mountains are less than 5 million years old with the youngest lava flows are possibly as recent as 50,000 years ago. The Wrangell volcanoes are among the highest mountains in North America and some of the largest (by volume) in the world.
Large volumes of ash were deposited 1250 and 1890 years ago from the eruption of Mount Churchill (the White River Ash).
Most of volcanoes of the Western Wrangell mountains are unlike other volcanoes located around the Pacific rim. Rather than erupting explosive lavas forming steep-sided cones, they have been built by the accumulation of hundreds of relatively fluid lava flows to form broad mountains with gentle slopes, typical of shield volcanoes. Now only youthful Mount Wrangell still displays a shield-like form; the other, generally older volcanoes have had much of their superstructure removed by glacial and other erosional processes. Eruptive activity has been noted in Mount Wrangell in 1784, 1884-5, and 1900. On clear, cold, and calm days, steam plumes are often visible.
1) USGS Alaska Volcano Observatory Website, January 2001
2) Kienle and Nye, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
3) U.S. National Park Service Website, Aniakchak National Monument and Preserve, 2000
4) U.S. National Park Service Website, Bering Land Bridge National Preserve, 2000
5) U.S. National Park Service Website, Katmai National Park and Preserve, 2000
6) Tilling, 1985, Volcanoes: USGS General Interest Publication
7) U.S. National Park Service Website, Lake Clark National Park and Preserve, 2000
8) U.S. National Park Service Website, Wrangell - St. Elias National Park and Preserve, 2000
9) U.S. National Park Service Website, Denali National Park and Preserve, 2004
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