Mount Adams (Washington)

Mount Adams is a stratovolcano in the Cascade Range and the second-highest mountain in the Pacific Northwest of North America (or third-highest, after Mount Rainier and Mount Shasta, if the latter is included). Adams is located in a remote wilderness approximately 35 miles (56 km) east of Mount St. Helens. The Mount Adams Wilderness only comprises the upper part of the volcano's cone. Adams' asymmetrical and broad body raises a mile and a half (2.4 km) above the Cascade crest and its nearly flat summit looks as if the volcano was decapitated (which it in fact has not been).

The Pacific Crest Trail traverses the west flank of Mt. Adams.

History

Native Americans in the area have created a detailed legend concerning the three smoking mountains that guard the Columbia River. According to their Bridge of the Gods tale, Wyeast (Mount Hood) and Pahto (Mount Adams; also called Paddo or Klickitat by natives) were the sons of Great Spirit. The brothers both competed for the love of the beautiful La-wa-la-clough (Mount St. Helens). When La-wa-la-clough chose Pahto, Wyeast struck his brother so hard that Pahto's head was flattened and Wyeast took La-wa-la-clough from him (thus attempting to explain Adams' squat appearance). However other versions of the story state that losing La-wa-la-clough caused Pahto such grief that he dropped his head in shame.

In 1805 the Lewis and Clark Expedition recorded seeing the mountain but they misidentified it as previously discovered and named Mt. St. Helens. This is the earliest recorded sighting of the volcano by European explorers.

Between 1830 to 1834 a man named Hall J. Kelley led a campaign to rename the Cascade Range to the President's Range and also to rename each major Cascade mountain after a former President of the United States. Mount Adams was not known to Kelley and was thus not in his plan. Mount Hood, in fact, was designated by Kelley to be renamed after President John Adams but a mistake by a mapmaker placed the Mount Adams name north of Mt. Hood and about 40 miles (60 km) east of Mt. St. Helens. By sheer coincidence there was in fact a large mountain there to receive the name. Since the mountain had no official name at the time the name stuck in spite of the fact that Kelley's renaming plan failed.

In 1901 local settler and mountaineer C. E. Rusk led noted glaciologist Harry Reid to Adams' remote location. Reid conducted the first systematic study of the volcano and also named its largest glaciers. Eighty years later the first official study of Adams by the USGS was carried out by survey geologists Wes Hildreth and Judy Fierstein. They concentrated their work on the volcanology of the mountain and the potential of the area to support geothermal power. Much of our knowledge of Adams comes from their survey work.

In 1929 and 1931 a man named Wade Dean filed mining claims to the sulfur on Adams' 210 acre (0.8 km²) summit plateau. After building a horse and mule trail they moved a diamond-tipped drilling machine to the summit area and proceeded to drill test pits. Although they did find sulfur sludge, the amount and quality of the ore was never good enough to make the venture profitable and the project was abandoned in 1959. Adams is the only High Cascade volcano to have its summit exploited by commercial miners.

Glaciers

Ice (mostly in the form of glaciers) covers about 6.2 mile² (16 km²) of the mountain's upper cone and is fed by ample snow and rainfall every year. Water percolates through the very porous interior of the main cone and exits near the volcano's base as springs.

Glaciers cover a total of 2.5% of Adams' surface but during the last ice age about 90% of the mountain had glaciers on it. Most of the largest extant glaciers (including the Adams, Klickitat, Lyman, Salmon, and White ) originate from Adams' summit ice cap. On the northwest face of the mountain is Adams Glacier, which cascades down a steep channel in a series of icefalls before spreading out and terminating at around 7000 feet (2100 m) elevation. At the head of the Klickitat Glacier on the volcano's eastern flank, a mile-wide cirque (second in size among the Cascades only to Carbon Glacier on Mount Rainier) is fed by two smaller glaciers from the summit ice cap and terminates around 6000 feet (1800 m).

Geology

Adams is made of several overlapping cones that together form an 18 mile (29 km) diameter base which is elongated in a north-south direction and covers an area of 250 mile² (650 km²). The volcano has a volume of 85 mile³ (350 km³) placing it second only to Mount Shasta in that category among the Cascade stratovolcanoes. Mount Adams was created by the subduction of the Juan de Fuca plate, which is located just off the coastline in the Pacific Northwest.

Mount Adams was born in relatively late Pleistocene time compared to most other Cascade Range volcanoes. Adams grew in several pulses of mostly lava-extruding eruptions. Each eruptive cycle was separated from one another by long periods of dormancy during which glaciers eroded the mountain to below 9000 feet (~2700 meters). Potassium-argon dating has identified two such eruptive periods; one 275,000 - 200,000 years ago and 150,000 - 100,000 years ago. Most of these eruptions and therefore most of the volcano, consisted of lava flows with little tephra. The loose material that makes up much of Adams' core is made of brecciated lava.

Andesite and basalt flows 20 to 200 feet (~6-61 meters) thick circle the base of the volcano (they filled existing depressions and ponded in valleys). Most of the volcano is made of andesite although a handful of dacite and pyroclastic flows erupted early in Adams' development. The present main cone was built when Adams was capped by a glacier system in the last ice age. The lava that erupted was shattered when it made contact with the ice and the cone interior is therefore made of easily eroded andesite fragments. Since its construction, constant emissions of heat and caustic gases have transformed much of the rock into clays (mostly kaolinite), iron oxides, sulfur-rich compounds and quartz.

The present main cone above 7000 feet (~2100 meters) was constructed sometime between 25,000 to 10,000 years ago. Since that time the volcano has erupted at least seven times (all of which were above 6500 feet or ~1980 meters). One of the most recent flows issued from South Butte and created the 4.5 mile long by half mile wide A.G. Aiken Lava Bed. This flow looks young but has 3500 year old Mount St. Helens ash on it meaning it is at least that old. The last lavas known to have erupted from Adams are the 2500 to 3500 year old Muddy Fork lava flows.

The Trout Lake Mudflow was the last large debris flow from Adams and the only large one since the end of the Ice Age. The flow dammed Trout Creek and covered 25 miles (~40 km) of the White Salmon River valley. Impounded water later formed Trout Lake. The Great Slide of 1921 started close to the headwall of the White Salmon Glacier and was the largest avalanche on Adams in historic time. The slide fell a mile (~1.6 km) and its debris covered one mile square of the upper Salt Creek area. Steam vents were reported active at the slide source for three years, leading to speculation that the event was started from a small steam explosion.

Since then, thermal anomalies (hot spots) and gas (including hydrogen sulfide) emissions especially on the summit plateau, indicate that Adams is dormant, not extinct. Future eruptions from Adams will probably follow patterns set by previous events and will thus be flank lava flows of andesite or basalt. Since the interior of the main cone is little more than a pile of fragmented lava and hydrothermally-altered rock, there is a potential for very large landslides and other debris flows.

Summit area

Contrary to legend, the flatness of Adams' current summit area is not due to the loss of the volcano's peak. Instead it was formed as a result of cone-building eruptions from separated vents. A false summit rises 11,500 feet (3,505 m) on the south side of the nearly half-mile (900 m) summit area. The true summit is about 800 ft (240 m) higher on the gently sloping north end (a small lava cone marks the highest point). Suksdorf Ridge is a long buttress trending from the false summit down to an elevation of 8000 ft (2,440 m). This structure was built by repeated lava flows in the late Pleistocene. The Pinacle forms the northwest false summit and was created by erosion from Adams and White Glaciers. The summit crater is filled with snow and is open on its west rim.

Area around Adams

Mount Adams is surrounded by a variety of other volcanic features and volcanos.

The largest flank volcano is a basaltic shield volcano on Adams east base called Goat Butte. This structure is at least 150,000 years old.
Little Mount Adams 450 ft (137 m) is a symmetrical cinder cone on top of the Ridge of Wonders on Adams' southeast flank.
Potato Hill is a cinder cone on Adams' north side that was created in the late Pleistocene and stands 800 ft (240 m) above its lava plain. Lavas from its base flowed into the Cispus Valley where they were later modified by glaciers.
At the 7,500 foot (2300 m) level on Adams' south flank is South Butte. The lavas associated with this structure are all younger than Suksdorf Ridge but were emplaced before the end of the ice age.
Located a few miles north of Adams is Goat Rocks; the heavily eroded ruins of a stratovolcano that is much older than Adams. Unlike Adams, the Goat Rocks Volcano was periodically explosive and deposited ash 2.5 million years ago that later solidified into 2,100 foot (640 m) thick tuff layers.
In the area surrounding Mt. Adams many underground caves have formed around inactive lava vents. These caves are usually close to the surface and can be hundreds of feet deep and wide.

Reference

Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X

External links

Stratovolcanoes | Mountains of Washington | Cascade Range | Volcanoes of Washington

Mount Adams | Mount Adams | Adams (sopka)

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