Novarupta

Site of the Largest Eruption of the 20th Century

Elevation

841 m

Last Eruption

1912

Type

Caldera

Country

United States

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

Pyroclastic flows and surges
Large explosive eruptions (VEI 4+)
Ash fall and tephra deposits
Lahars and debris flows

Risk Level

Population at RiskModerate

Infrastructure RiskHigh

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	114 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

Related Volcanoes

All United States Volcanoes

Other Volcanoes in United States

Akutan
Stratovolcano
Crater Lake
Caldera
Kilauea
Shield volcano
Mauna Loa
Shield volcano

Interesting Facts

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The 1912 Novarupta eruption ejected roughly 13–15 km³ of magma — approximately 30 times the volume of the 1980 Mount St. Helens eruption.

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Despite being the largest eruption of the 20th century, the 1912 event killed no one directly, owing to the extreme remoteness of the Alaska Peninsula.

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For over 40 years after the eruption, scientists incorrectly attributed it to Mount Katmai rather than to the Novarupta vent 10 km away.

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The pyroclastic flows from the 1912 eruption filled the Valley of Ten Thousand Smokes to depths of up to 213 m (700 ft) — deeper than the height of most skyscrapers.

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The eruption column reached an estimated 20–25 km into the stratosphere, and ashfall darkened Kodiak Island (160 km away) for three consecutive days.

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Novarupta's lava dome — 65 m high and 400 m wide — represents the final plug of rhyolitic magma that sealed the vent at the eruption's end.

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The name 'Novarupta' is Latin for 'newly erupted,' reflecting that the vent did not exist before the 1912 eruption.

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Mount Katmai's summit collapsed into a 3 × 4 km caldera during the eruption as magma drained 10 km underground from Katmai's reservoir toward Novarupta — one of the most dramatic examples of lateral magma transport ever documented.

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The 1912 eruption caused the creation of Katmai National Monument in 1918, one of the earliest U.S. national monuments established for its volcanic significance.

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At its peak, the eruption rate has been estimated at 170,000 m³ per second — enough to fill a football stadium in under a second.

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The eruption produced three compositionally distinct phases: rhyolite, dacite, and andesite, reflecting the progressive tapping of deeper magma as the chamber emptied.

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Acid rainfall from the eruption etched cloth and corroded metal hardware on Kodiak Island, and sulfurous fumes were detectable hundreds of kilometers away.

Frequently Asked Questions

What was the Novarupta eruption of 1912?

The Novarupta eruption of June 6–8, 1912, was the largest volcanic eruption of the 20th century, rated VEI 6 on the Volcanic Explosivity Index. It ejected approximately 13–15 km³ of magma from a vent on the Alaska Peninsula, generating massive pyroclastic flows that created the Valley of Ten Thousand Smokes — a valley filled with up to 213 m of volcanic ash and pumice. The eruption also caused the collapse of nearby Mount Katmai into a 3 × 4 km caldera, as magma drained laterally underground from Katmai's reservoir toward the Novarupta vent. Despite its enormous power — roughly 30 times larger than the 1980 Mount St. Helens eruption — no one was killed, due to the area's extreme remoteness.

Is Novarupta still active?

Novarupta is classified as active by the Smithsonian Global Volcanism Program, though its single eruption occurred in 1912 and the vent is now sealed by a rhyolitic lava dome. The specific Novarupta vent is unlikely to reactivate at the same location, but the broader Katmai volcanic cluster — including Mount Katmai, Trident, Mageik, and Martin — sits atop an interconnected magmatic system that remains fully capable of future eruptions. The Alaska Volcano Observatory monitors the entire cluster with seismometers and satellite imagery. Currently, the Katmai area carries an Aviation Color Code of Green, indicating normal background activity.

Why was the 1912 eruption attributed to Katmai instead of Novarupta?

When the 1912 eruption occurred, the Alaska Peninsula was so remote that no direct observations of the vent were possible. Observers on Kodiak Island and passing ships saw an enormous eruption column but could not determine which peak was its source. Mount Katmai's summit had collapsed into a dramatic caldera, making it the obvious suspect. It was not until the 1950s and 1960s that field geologists — particularly Garniss Curtis — demonstrated through detailed mapping and petrology that the eruption products radiated from the Novarupta vent, not from Katmai. The discovery that magma had migrated 10 km underground from Katmai to Novarupta was revolutionary and fundamentally changed understanding of how large eruptions can drain distant magma chambers.

What is the Valley of Ten Thousand Smokes?

The Valley of Ten Thousand Smokes is a 20-km-long, 5-km-wide valley on the Alaska Peninsula that was filled by pyroclastic flows during the 1912 Novarupta eruption. The flows deposited up to 213 m (700 ft) of incandescent ash-flow tuff, burying the former river valley completely. When explorer Robert Griggs reached the valley in 1916, he found thousands of fumaroles — steam vents rising from the still-hot deposit — and gave the valley its evocative name. The fumaroles gradually diminished as the deposit cooled and had largely ceased by the 1950s. Today the valley floor is a barren, windswept expanse deeply incised by river erosion, accessible via a seasonal bus tour from Brooks Camp in Katmai National Park.

How does Novarupta compare to Mount St. Helens?

The 1912 Novarupta eruption was approximately 30 times larger than the 1980 Mount St. Helens eruption in terms of magma volume. Novarupta ejected 13–15 km³ of magma (VEI 6) compared to St. Helens' roughly 0.5 km³ (VEI 5). The Novarupta pyroclastic flows covered 140 km² and filled a valley to 213 m depth; St. Helens' lateral blast devastated about 600 km² but deposited far less material. St. Helens killed 57 people; Novarupta killed none. The disparity in fame largely reflects timing and proximity: St. Helens erupted near populated areas in the television age, while Novarupta erupted in one of the most remote places in North America.

Can you visit Novarupta?

Yes, though reaching Novarupta requires significant effort. It is located within Katmai National Park and Preserve on the Alaska Peninsula, accessible only by air. Visitors fly from Anchorage to King Salmon, then take a floatplane to Brooks Camp. From Brooks Camp, the National Park Service runs a seasonal bus tour along a 37-km unpaved road to the Three Forks Overlook at the edge of the Valley of Ten Thousand Smokes. Reaching the Novarupta dome itself requires a full-day or multi-day backcountry hike (approximately 10 km from the overlook) with no maintained trails, requiring bear-country preparedness and off-trail navigation skills. The hiking season runs from late June through mid-September.

How big was the Novarupta eruption compared to other major eruptions?

The 1912 Novarupta eruption was the largest of the 20th century and ranks among the five largest eruptions in recorded human history. At VEI 6, it was comparable to the 1883 Krakatau and 1991 Pinatubo eruptions but significantly smaller than the 1815 Tambora eruption (VEI 7). In terms of ejecta volume, Novarupta produced approximately 17 km³ of tephra — more than Pinatubo (~10 km³) but far less than Tambora (~150 km³). The eruption was roughly ten times larger than Pinatubo and thirty times larger than the 1980 Mount St. Helens eruption. It ranks behind only Tambora, Krakatau, and the ~1600 BCE Minoan eruption of Santorini among historical eruptions.

What caused Mount Katmai's caldera to collapse during the 1912 eruption?

Mount Katmai's summit collapsed into a 3 × 4 km caldera because the eruption at Novarupta — 10 km away — drained magma from a reservoir beneath Katmai through an underground lateral conduit. As enormous volumes of magma were evacuated from Katmai's subsurface reservoir and erupted at the Novarupta vent, the unsupported summit of Katmai collapsed under its own weight. This process is analogous to pulling a plug from beneath a sandcastle. The resulting caldera dropped roughly 1 km and now holds a turquoise lake approximately 250 m deep. The lateral magma drainage was not understood until decades later and remains one of the most important discoveries in modern volcanology.