Mount Rainier in the context of Base camp

A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 kilometres (5 miles).

The term composite volcano is used because strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State, US, and Mount Pinatubo (1991) in the Philippines have erupted catastrophically, but with fewer deaths.

A snow field, snowfield or neve is an accumulation of permanent snow and ice, typically found above the snow line, normally in mountainous and glacial terrain.

Glaciers originate in snowfields. The lower end of a glacier is usually free from snow and névé in summer. In the upper end and above the upper boundary of a glacier, the snow field is an ice field covered with snow. The glacier upper boundary, where it emerges from under a snow field, is ill-defined because of gradual transition.

Washington is a state in the Pacific Northwest region of the United States. It is often referred to as Washington state to distinguish it from the national capital, both named after George Washington, a U.S. Founding Father and the first U.S. president. Washington borders the Pacific Ocean to the west, Oregon to the south, and Idaho to the east and shares an international border with the Canadian province of British Columbia to the north. Olympia is the state capital, and the most populous city is Seattle.

Washington is the 18th-largest state, with an area of 71,362 square miles (184,830 km), and the 13th-most populous state, with a population of just less than 8 million. The majority of Washington's residents live in the Seattle metropolitan area, the center of transportation, business, and industry on Puget Sound, an inlet of the Pacific Ocean consisting of numerous islands, deep fjords and bays carved out by glaciers. The remainder of the state consists of deep temperate rainforests in the west; mountain ranges in the west, center, northeast, and far southeast, and a semi-arid basin region in the east, center, and south, given over to intensive agriculture. Washington is the second most populous state on the West Coast and in the Western United States, after California. Mount Rainier, an active stratovolcano, is the state's highest elevation at 14,411 feet (4,392 meters), and is the most topographically prominent mountain in the contiguous U.S.

Mountaineering, mountain climbing, or alpinism is a set of outdoor activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas that have become sports in their own right. Indoor climbing, sport climbing, and bouldering are also considered variants of mountaineering by some, but are part of a wide group of mountain sports.

Unlike most sports, mountaineering lacks widely applied formal rules, regulations, and governance; mountaineers adhere to a large variety of techniques and philosophies (including grading and guidebooks) when climbing mountains. Numerous local alpine clubs support mountaineers by hosting resources and social activities. A federation of alpine clubs, the International Climbing and Mountaineering Federation (UIAA), is the International Olympic Committee-recognized world organization for mountaineering and climbing. The consequences of mountaineering on the natural environment can be seen in terms of individual components of the environment (land relief, soil, vegetation, fauna, and landscape) and the location/zone of mountaineering activity (hiking, trekking, or climbing zone). Mountaineering impacts communities on economic, political, social, and cultural levels, often leading to changes in people's worldviews influenced by globalization, specifically foreign cultures and lifestyles.

The Cascade Range, or Cascades, is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as many of those in the North Cascades, and the notable volcanoes known as the High Cascades. The small part of the range in British Columbia is referred to as the Canadian Cascades or, locally, as the Cascade Mountains. The highest peak in the range is Mount Rainier in Washington at 14,411 feet (4,392 m).

The Cascades are part of the Pacific Ocean's Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the eruptions in the contiguous United States over the last 200 years have been from the Cascade Volcanoes. The two most recent were Lassen Peak from 1914 to 1921 and a major eruption of Mount St. Helens in 1980. Minor eruptions of Mount St. Helens have also occurred since, most recently from 2004 to 2008. The Cascade Range is a part of the American Cordillera, a nearly continuous chain of mountain ranges (cordillera) that form the western "backbone" of North, Central, and South America.

Northern California (commonly shortened to NorCal) is a geocultural region that comprises the northern portion of the U.S. state of California, spanning the northernmost 48 of the state's 58 counties. Northern California in its largest definition is determined by dividing the state into two regions, the other being Southern California. The main northern population centers include the San Francisco Bay Area (anchored by the cities of San Jose, San Francisco, and Oakland), the Greater Sacramento area (anchored by the state capital Sacramento), the Redding, California, area south of the Cascade Range, and the Metropolitan Fresno area (anchored by the city of Fresno). Northern California is coterminous with the natural range of the coast redwood and the giant sequoia, with many well-known old-growth forests and smaller groves. It contains most of the Sierra Nevada, including Yosemite Valley and part of Lake Tahoe, Mount Shasta (the second-highest peak in the Cascade Range after Mount Rainier in Washington), and most of the Central Valley, one of the world's most productive agricultural regions. Northern California is also home to Silicon Valley, the global headquarters for several of the largest most powerful companies in the world, including Alphabet Inc. (Google), Apple, Meta, and Nvidia.

The Northern California Megaregion, one of the 11 megaregions of the United States is centered in Northern California, and extends from Metropolitan Fresno north to Greater Sacramento, and from the Bay Area east across the Nevada state line to encompass the entire Lake Tahoe–Reno area.

Penitentes, or nieves penitentes (Spanish for "penitent snows"), are snow formations found at high altitudes. They take the form of elongated, thin blades of hardened snow or ice, closely spaced and pointing towards the general direction of the sun.

The name comes from the resemblance of a field of penitentes to a crowd of kneeling people doing penance. The formation evokes the tall, pointed habits and hoods worn by brothers of religious orders in the Processions of Penance during Spanish Holy Week. In particular, the brothers' hats are tall, narrow, and white, with a pointed top.

Mount Rainier National Park (/reɪ.ˈnɪər/ ray-NEER) is a national park of the United States located in southeast Pierce County and northeast Lewis County in the U.S. state of Washington. The park was established on March 2, 1899, as the fourth national park in the United States, preserving 236,381 acres (369.3 sq mi; 956.6 km) including all of Mount Rainier, a 14,410-foot (4,390 m) stratovolcano. The mountain rises abruptly from the surrounding land with elevations in the park ranging from 1,600 feet to over 14,000 feet (490–4,300 m). The highest point in the Cascade Range, Mount Rainier is surrounded by valleys, waterfalls, subalpine meadows, and 91,000 acres (142.2 sq mi; 368.3 km) of old-growth forest. More than 25 glaciers descend the flanks of the volcano, which is often shrouded in clouds that dump enormous amounts of rain and snow.

The park has several entrances that lead to three general areas: Paradise, the Carbon River and Mowich Lake area, and Sunrise. It had over 1.6 million visitors in 2024. Mount Rainier is circled by the Wonderland Trail and is covered by glaciers and snowfields totaling about 35 square miles (91 km). Carbon Glacier is the largest glacier by volume in the contiguous United States, while Emmons Glacier is the largest glacier by area. Mount Rainier is a popular peak for mountaineering with some 10,000 attempts per year with approximately 50% making it to the summit.

The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 miles (1,100 km). The arc formed due to subduction along the Cascadia subduction zone. Although taking its name from the Cascade Range, this term is a geologic grouping rather than a geographic one, and the Cascade Volcanoes extend north into the Coast Mountains, past the Fraser River which is the northward limit of the Cascade Range proper.

Some of the major cities along the length of the arc include Portland, Seattle, and Vancouver, and the population in the region exceeds 10 million. All could be potentially affected by volcanic activity and great subduction-zone earthquakes along the arc. Because the population of the Pacific Northwest is rapidly increasing, the Cascade volcanoes are some of the most dangerous, due to their eruptive history and potential for future eruptions, and because they are underlain by weak, hydrothermally altered volcanic rocks that are susceptible to failure. Consequently, Mount Rainier is one of the Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study, due to the danger it poses to Seattle and Tacoma. Many large, long-runout landslides originating on Cascade Volcanoes have engulfed valleys tens of kilometers from their sources, and some of the areas affected now support large populations.

The Seattle metropolitan area is an urban conglomeration in the U.S. state of Washington that comprises Seattle, its surrounding satellites and suburbs. The United States Census Bureau defines the Seattle–Tacoma–Bellevue, WA metropolitan statistical area as the three most populous counties in the state: King, Pierce, and Snohomish. Seattle has the 15th largest metropolitan statistical area (MSA) in the United States with a population of 4,018,762 as of the 2020 census, over half of Washington's total population.

The area is considered part of the greater Puget Sound region, which largely overlaps with the Seattle Combined Statistical Area (CSA). The Seattle metropolitan area is home to a large tech industry and is the headquarters of several major companies, including Microsoft and Amazon. The area's geography is varied and includes the lowlands around Puget Sound and the Cascade Mountains; the highest peak in the metropolitan area is Mount Rainier, which has a summit elevation of 14,411 feet (4,392 m) and is one of the tallest mountains in the United States.

The Puyallup River (/pjuːˈæləp/ pyew-AL-əp) is a river in the U.S. state of Washington. About 45 miles (72 km) long, it is formed by glaciers on the west side of Mount Rainier. It flows generally northwest, emptying into Commencement Bay, part of Puget Sound. The river and its tributaries drain an area of about 948 square miles (2,460 km) in Pierce County and southern King County.

The lower, northwestern half of the river's watershed is a complex amalgam of glacial and tectonic features dating back to the Pleistocene, as well as more recent (Holocene) changes caused by a series of lahars which flowed down from Mount Rainier between 5,600 and 800 years Before Present. The valley's 150,000 residents are at risk from future lahars. For this reason, the United States Geological Survey has installed a lahar warning system.

The Carbon River is a river in the U.S. state of Washington. It flows about 30 miles (48 km) from its source, the Carbon Glacier on Mount Rainier, to join the Puyallup River at Orting.

Charles Wilkes called the river the "Upthascap River", but after the discovery of coal along its banks in 1876 the river was renamed "Carbon".

The White River is a white, glacial river in the U.S. state of Washington. It flows about 75 miles (121 km) from its source, the Emmons Glacier on Mount Rainier, to join the Puyallup River at Sumner. It defines part of the boundary between King and Pierce counties.

The Nisqually River /nɪˈskwɑːli/ is a river in west central Washington in the United States, approximately 81 miles (130 km) long. It drains part of the Cascade Range southeast of Tacoma, including the southern slope of Mount Rainier, and empties into the southern end of Puget Sound. Its outlet was designated in 1971 as the Nisqually Delta National Natural Landmark.

The Nisqually River forms the Pierce–Lewis county line, as well as the boundary between Pierce and Thurston counties.

The Cowlitz River is a river in the state of Washington in the United States, a tributary of the Columbia River. Its tributaries drain a large region including the slopes of Mount Rainier, Mount Adams, and Mount St. Helens.

The Cowlitz has a 2,586-square-mile (6,698 km) drainage basin, located between the Cascade Range in eastern Lewis County, Washington and the cities of Kelso and Longview. The river is roughly 105 miles (169 km) long, not counting tributaries.