Mount Rainier

America's Most Dangerous Volcano

Elevation

4,392 m

Last Eruption

~1450 CE

Type

Stratovolcano

Country

United States

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

Pyroclastic flows
Lava flows
Volcanic bombs and ballistics
Lahars and mudflows

Risk Level

Population at RiskModerate

Infrastructure RiskModerate

Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary

Unknown

Silica Content

Varied composition

Tectonic Setting

Unknown

Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch

Unknown

Evidence

Unknown

Eruption Statistics & Analysis

Metric	Value	Global Ranking	Significance
Total Recorded Eruptions	Unknown	Low	Moderately active volcano
Maximum VEI	VEI Unknown	Minor	Local impact potential
Recent Activity	576 years ago	Historical	Historically active

Monitoring & Alert Status

Monitoring Networks

USGS Volcano Hazards Program

Comprehensive monitoring network

Global Volcanism Program

International eruption database

Current Status

Normal

No recent activity. Routine monitoring continues.

Authority Sources

Smithsonian GVP

Official volcano database

USGS Volcano Hazards

U.S. Geological Survey

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snow covered mountain under blue sky during daytime

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Interesting Facts

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Mount Rainier carries more glacial ice than all other Cascade Range volcanoes combined — 26 named glaciers covering 93 km² (36 sq mi).

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The Osceola Mudflow ~5,600 years ago deposited 3.8 km³ of debris — enough to bury Manhattan under 40 m (130 ft) of mud — making it one of the largest lahars in geological history.

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Between 80,000 and 150,000 people live directly atop ancient lahar deposits in the river valleys radiating from Mount Rainier.

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The summit's volcanic glacier-cave system, melted by geothermal heat, extends nearly 3.2 km and is the largest of its kind in the world.

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A crater lake at 4,329 m (14,203 ft) elevation inside the west summit crater is the highest lake in North America — accessible only through ice caves.

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Mount Rainier carries approximately eight times as much glacial ice as Nevado del Ruiz had in 1985, when a lahar killed over 23,000 people in Armero, Colombia.

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The Electron Mudflow reached the Puget Sound lowlands only ~500 years ago without any volcanic eruption — triggered solely by the collapse of hydrothermally weakened rock.

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A lahar from Rainier's west flank could reach the town of Orting (pop. ~8,000) in approximately 60 minutes, and the Nisqually park entrance in just 10 minutes.

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Paradise, on Rainier's south flank, holds the contiguous US record for measured seasonal snowfall: 28.5 m (93.5 ft) in 1971–72.

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Over 439,000 people summited Mount Rainier between 1950 and 2018, making it one of the most-climbed glaciated peaks in the world.

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Mount Rainier is one of only 16 Decade Volcanoes worldwide — selected by the IAVCEI for their exceptional combination of hazard and population risk.

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In July 2025, a seismic swarm produced over 540 located earthquakes beneath the summit in a single week — the largest swarm since 2009.

Frequently Asked Questions

Is Mount Rainier an active volcano?

Yes, Mount Rainier is classified as an active volcano by both the USGS and the Smithsonian Institution's Global Volcanism Program. Its last confirmed eruption occurred around 1450 CE, and uncertain phreatic (steam-driven) activity was reported as recently as 1894. Volcanologists define 'active' as having erupted within the Holocene (past ~11,700 years), and Rainier has produced at least 24 recognized eruptions during this period. The volcano is continuously monitored by the USGS Cascades Volcano Observatory, and a swarm of over 540 earthquakes beneath the summit in July 2025 demonstrated that the volcanic system remains dynamic. Another eruption is considered certain on a geological timescale.

When did Mount Rainier last erupt?

Mount Rainier's last confirmed eruption occurred approximately 1450 CE, based on tree-ring dating of tephra deposits found on the volcano's flanks. Several 19th-century eruptions were reported by observers in Seattle and Tacoma — including events in 1854, 1870, 1879, 1882, and 1894 — but none have been confirmed by identifiable eruptive deposits. The most credible of these, a probable phreatic eruption in 1894, remains officially uncertain. The Smithsonian Global Volcanism Program lists 1450 CE as the last known eruption. The current repose period of approximately 575 years is notable but not unprecedented in Rainier's eruptive history.

Could Mount Rainier erupt again?

Mount Rainier will almost certainly erupt again. The volcano has averaged roughly one eruption per century over the past 2,600 years, and its current dormancy of ~575 years, while longer than average, falls well within the range of historical repose intervals. The USGS considers future eruptions inevitable on a geological timescale, though predicting the timing of any specific eruption is not currently possible. A future eruption would most likely involve moderate explosive activity (VEI 2–4) with lahars as the primary threat. However, even without an eruption, a catastrophic lahar could be triggered by gravitational collapse of the hydrothermally weakened summit — as the Electron Mudflow demonstrated only ~500 years ago.

Why is Mount Rainier considered so dangerous?

Mount Rainier is considered one of the most dangerous volcanoes in the United States — and the world — due to a convergence of factors. First, 26 glaciers and 93 km² of permanent ice provide enormous volumes of meltwater that can mix with volcanic debris to form devastating lahars. Second, extensive hydrothermal alteration has converted large portions of the upper mountain to weak, water-saturated clay, making it prone to catastrophic collapse even without an eruption. Third, approximately 80,000–150,000 people live directly in mapped lahar inundation zones. Fourth, warning time is extremely limited — as little as 60 minutes for a major lahar to reach populated lowlands. The USGS ranked Rainier as the third most hazardous U.S. volcano in its 2018 assessment.

What is a lahar and why are Rainier's lahars so dangerous?

A lahar is a rapidly flowing slurry of water, volcanic rock, and debris that moves like liquid concrete at speeds of 30–80 km/h (20–50 mph), destroying or burying everything in its path. Lahars at Mount Rainier form when glacial meltwater mixes with volcanic material during eruptions, or when hydrothermally weakened sections of the mountain collapse under gravity. Rainier's lahars are exceptionally dangerous because they can be enormous (the Osceola Mudflow moved 3.8 km³ of material), they travel far (reaching Puget Sound, over 100 km away), and densely populated communities like Orting, Puyallup, and Sumner lie directly in their paths. The Electron Mudflow ~500 years ago proved that catastrophic lahars can occur without any eruption.

How tall is Mount Rainier?

Mount Rainier stands 4,392 m (14,411 ft) above sea level, making it the highest peak in the Cascade Range and the most topographically prominent mountain in the contiguous United States. It rises roughly 4,000 m above the surrounding Puget Sound lowlands. The summit was once even taller — possibly reaching approximately 4,900 m (16,000 ft) — before the catastrophic sector collapse ~5,600 years ago that generated the Osceola Mudflow removed the upper northeast flank. The present summit cone was rebuilt within the resulting amphitheater.

What type of volcano is Mount Rainier?

Mount Rainier is a stratovolcano, also called a composite volcano — a steep-sided, roughly conical mountain built by alternating layers of lava flows, pyroclastic material, and volcanic debris over hundreds of thousands of years. Rainier is composed primarily of andesite, an intermediate-composition volcanic rock typical of subduction-zone volcanism, along with some basalt and dacite. The volcano formed due to subduction of the Juan de Fuca Plate beneath the North American Plate along the Cascadia Subduction Zone. At over 500,000 years old, it has been significantly modified by glacial erosion and a massive sector collapse.

Can you visit Mount Rainier?

Yes, Mount Rainier National Park — established in 1899 as the fifth U.S. national park — is open year-round and receives over 2 million visitors annually. The most popular areas are Paradise (south side) with wildflower meadows and views, and Sunrise (northeast) at 1,950 m, the highest point accessible by car. The park offers over 420 km of trails including the 150 km Wonderland Trail. Summit climbing requires technical glacier skills and permits; guided climbs are available. The entrance fee is $30 per vehicle (2025). Visitors should be aware of lahar hazard evacuation routes in valley areas.

What was the Osceola Mudflow?

The Osceola Mudflow was a catastrophic lahar approximately 5,600 years ago when Mount Rainier's summit and upper northeast flank collapsed during volcanic eruptions. The debris avalanche transformed into a mudflow carrying 3.8 km³ of material — at least ten times larger than any other known Rainier lahar. It surged down the White River valley past modern-day Enumclaw and reached Puget Sound near present-day Tacoma and Auburn, covering 550 km². Deposits are up to 30 m deep in lowland areas. The collapse removed roughly 2.0–2.5 km³ from the summit. It remains one of the largest documented lahars on Earth.

How far is Mount Rainier from Seattle?

Mount Rainier is approximately 87 km (54 mi) southeast of downtown Seattle and a similar distance from Tacoma. On clear days, the volcano's 4,392 m summit dominates the southeastern skyline. The drive from Seattle to the Nisqually entrance of Mount Rainier National Park takes approximately 2 hours via State Route 7. While Seattle itself is unlikely to be directly impacted by a lahar, communities in the Kent Valley, Puyallup River valley, and other lowland areas between the volcano and the cities lie within mapped lahar hazard zones.