Glacier Peak

Remnants of past (prehistoric) lava domes are main components of the summit of the volcano, in addition to its false summit, Disappointment Peak. Past pyroclastic flow deposits are easily visible in river valleys near the volcano, likely caused by lava dome collapse, along with ridges found east of the summit consisting of ash cloud remains.[6] On its western flank, the volcano also has a lahar, or mudflow deposit, which runs for about 22 miles (35 km) into the White Chuck River Valley around 14,000 years ago. Ten other pyroclastic flow deposits are visible, all identified as relatively 10,000 years old. There is also a considerably newer mudflow, about 5,500 years old, which covers an area of 9.3 mi (15 km) between the same river valley, along with two small incidents both under 3,000 years old. Another lahar, of unidentified age, was rich in oxyhornblende dacite; and continued for 30 km (19 mi) into the Sauk River.[7]

There are also ash cloud deposits on the opposite eastern flank of the volcano. Studies of the mountain have to date been unable to find any correspondence with pyroclastic flows, but several past mudflows have been identified. In the Dusty Creek, located by the mountain, there is a lahar at least 98 ft (30 m) thick, containing pyroclastic flow deposits and other mudflows. However, this large mudflow is part of a 980-foot-thick (300 m) concentration of past incidents at the volcano that spans the Dusty and Chocolate Creek. In the area at least 2.4 cubic miles (10 km³) of lithic debris are contained.[7] Tephra deposits are for the most part constrained to the left flank of the volcano, and at least nine past incidents have been identified. These form several layers of tephra constructing the mountain. Smaller eruptions involving tephra occurred between 6,900 and 5,500 years ago, again between 3,450 and 200 years ago, and as recently as 316 to 90 years ago.[7]

On the mountain, about 5,900 ft (1,800 m) up, are three additional cinder cones — one at the head of White Chuck River, one at Dishpan Gap, and one near Indian Pass.[8] The volcano has also caused thermal events such as hot springs. There were three hot springs on the mountain: Gamma, Kennedy, and Sulphur,[3] but Kennedy Hot Springs was destroyed and buried in a slide.[9]

Tectonic setting

Diagram of plate tectonics for Cascade Range

The volcano is located in Washington, and is one of the five major stratovolcanoes there. Situated in the Cascade Volcanic Arc, the volcano was created by subduction of the oceanic Juan de Fuca Plate under the North American Plate.[10] Convergence between the two continues at a rate of 1.6 inches (4 cm) per year. This range has been volcanically active for about 36 million years, and the rocks that make up its volcanoes are between 55 and 42 million years old. Eruptions within the range are irregular and do not occur all at once. In an attempt to organize the volcanoes by age, scientists typically divide them into the High Cascades, younger volcanoes, and the Western Cascades, consisting of the older volcanoes. However, the vents in Washington are all of different ages so none of its volcanoes are included in either of the sections.[11]

Around the area, there were many Native Americans, and along with other Washington volcanoes, the mountain was recognized by them as a spirit. When European-American explorers reached the area, they learned about the mountain, though only partially, through local legends. Although the local people described Glacier Peak as a vital part of their storytelling and beliefs; when other volcanoes in the area were mapped, Glacier Peak was left out. In 1850 natives mentioned the volcano to naturalist George Gibbs saying that the volcano had once "smoked".[6] In 1898 the volcano was finally documented on a map.[6]

Native Americans also used the area around the Cascades for their agriculture, leading them to often congregate in the region. As a result, gold miners eventually reached the area in the 1870s–1890s, searching for resources and rich land. The first white man recorded to observe the mountain—Daniel Lindsley—was an employee of the Northern Pacific Railroad Company searching for possible railroad routes when he saw it in 1870.[12]

Despite its elevation of 10,541 feet (3,213 m), Glacier Peak is a small stratovolcano. Its relatively high summit is a consequence of its location atop a high ridge, but its volcanic portion extends only 1,600–3,200 feet (500–1,000 m) above the underlying ridge.[13] Another Cascade Arc volcano with similar geomorphology is the Mount Meager massif in southwestern British Columbia, Canada, which is situated on a 1,300 ft (400 m) ridge of nonvolcanic, crystalline and metamorphic rock.[14]

View from Liberty Cap across the Suiattle River Valley

Of the five major volcanoes in Washington, only Glacier Peak and Mount St. Helens have had large eruptions in the past 15,000 years. Since both volcanoes generate magma of dacitic origin, the viscous magma builds up since it cannot flow through the eruptive vent. Gradually, the pressure grows, culminating in an explosion that ejects materials such as tephra, which in its simplest form, is ash.[6]

Tephrochronology and radiocarbon dating indicate that Glacier Peak eruptions occurred in 1700 AD ± 100 years, 1300 AD ± 300 years, 900 AD ± 50 years, 200 AD ± 50 years, 850 BC, 3150 BC, and in 3550 BC. The Volcanic Explosivity Index (VEI) for three of these was 2 to 4, small compared to the 5 of the 1980 eruption of Mount St. Helens. They were characterized mainly by a central vent eruption, followed by an explosive eruption. These eruptions varied in outcome; some produced lahars, some pyroclastic flows, and others lava domes.[3]

A little more than 13,000 years ago, a sequence of nine tephra eruptions occurred within a period of less than a few hundred years. Associated with these eruptions were pyroclastic flows. Mixed with snow, ice and water, these formed lahars that raced into three nearby rivers, filling their valleys with deep deposits. Subsequently, the mudflows drained into both the North Fork of the Stillaguamish River (at that time an outlet of the Sauk River) and Skagit Rivers. In Arlington, 60 miles (97 km) downstream, lahars deposited seven feet of sediment. Subsequent erosion of lahar deposits near Darrington led to the current river system with the Stillaguamish River separated from the Sauk/Skagit Rivers. Lahar debris was deposited along both the Skagit and Stillaguamish Rivers all the way to Puget Sound. A small portion of the erupted tephra was deposited locally. However, most of the tephra reached higher levels of the atmosphere, and was transported by the wind hundreds of miles. Deposits from this congregation were as thick as 1 foot (0.30 m) near Chelan and 0.3 inches (7.6 mm) near Missoula, Montana.[6] The table below shows the three largest eruptions from this sequence.[15]

Since these events, Glacier Peak has produced several lahars. The largest mudflows were 5,900 and 1,800 years ago and were associated with dome-building eruptions. In both cases, the lahars traveled down the Skagit River to Puget Sound.[6]

Hazards

Glacier Peak from the southeast

The risk of an eruption in any given year is currently estimated as 1 in 1,000.[16] As of 2018, Glacier Peak is classified as one of the 18 most dangerous volcanoes in the United States.[17]

When lahars reach populated areas, they can bury structures and people. An example was the Armero tragedy at Nevado del Ruiz where 23,000 died from an enormous mudflow. Lahars from Glacier Peak pose a similar threat to the small communities of Darrington and Concrete and a lesser threat to the larger and rapidly growing towns of Mount Vernon and Burlington, as well as other communities along the lower Skagit and Stillaguamish Rivers.[6] A 2005 study conducted by the United States Geological Survey identified nine Cascade volcanoes, including Glacier Peak, as "very-high-threat volcanoes with inadequate monitoring". At the time of the study, only one seismometer was installed on Glacier Peak that had not "worked in two years".[18] As of 2023, the PNSN still operates only one seismometer on Glacier Peak.[19]

In 2018, the USGS applied to add four more stations, but regulations protecting federal wilderness areas prohibit the use of helicopters that are needed to transport materials; advocacy groups opposed an exemption for the project and filed objections.[20][21] In 2019, Congress passed the National Volcano Early Warning and Monitoring System Act to authorize more monitoring stations, but did not include funding to construct them.[22] Permits were granted by the U.S. Forest Service in June 2022.[23]

The Pacific Crest Trail passes near Glacier Peak. The Suiattle River crossing is a well-known feature on the Pacific Crest Trail (PCT) as it passes through the area. The Suiattle PCT crossing used to have a bridge crossing until it was flooded out by storms in late 2003.[26]

The first recorded person to climb the mountain was Thomas Gerdine, along with a group of United States Geological Survey scientists, Sam Strom, A. H. Dubor, and Darcy Bard, in 1897.[4] The climb is Alpine Grade I or II.[27]

The easiest ski route is about 5 miles (8.0 km) of walking along the White Chuck River Trail (Forest Service Trail No. 643) and up the Sitkum Glacier. The trail is reached via Forest Service Road No. 23. The Sitkum Glacier ski route is rated blue to black diamond for both the ascent and the descent.[28]

The Seattle-based composer, Alan Hovhaness, dedicated his Symphony no.66 as "Hymn to Glacier Peak": see Symphony no.66 (Hovhaness).

• List of mountain peaks of North America
  • List of mountain peaks of the United States
    • List of mountain peaks of Washington (state)
      • List of highest points in Washington by county
• List of Ultras of the United States
• List of volcanoes in the United States

• Glacier Peak on Ski Mountaineer.com
• "Glacier Peak". Peakware.com. Archived from the original on March 4, 2016.
• "Glacier Peak". SummitPost.org.
• University of Washington Libraries Digital Collections – The Mountaineers Collection Photographic albums and text documenting the Mountaineers official annual outings undertaken by club members from 1907 to 1951, primarily on the Olympic Peninsula, in Mount Rainier National Park and on Glacier Peak.