DESCRIPTION:
1912 Eruption of Novarupta, Alaska

[Map,30K,InlineGIF]
Location map for Novarupta and the Valley of Ten Thousand Smokes, Katmai National Park, Alaska, showing the 120-cubic-kilometer extent of the 1912 ash-flow sheet.
-- Modified from: Hildreth, 1983, IN: JVGR, v.18

The June 1912 eruption of Novarupta Volcano altered the Katmai area dramatically. Severe earthquakes rocked the area for a week before Novarupta exploded with cataclysmic force. Enormous quantities of hot, glowing pumice and ash were ejected from Novarupta and nearby fissures. This material flowed over the terrain, destroying all life in its path. Trees up slope were snapped off and carbonized by the blasts of hot wind and gas. For several days ash, pumice, and gas were ejected and a haze darkened the sky over most of the Northern Hemisphere. When it was over, more than 40 square miles of lush green land lay buried beneath volcanic deposits as much as 700 feet deep. At nearby Kodiak, for two days a person could not see a lantern held at arm's length. Acid rain caused clothes to disintegrate on clotheslines in distant Vancouver, Canada. The eruption was ten times more forceful than the 1980 eruption of Mount St. Helens. In the valleys of Knife Creek and the Ukak River, innumerable small holes and cracks developed in the volcanic ash deposits, permitting gas and steam from the heated groundwater to escape. It was an apparently unnamed valley whehn the 20th century's most dramatic volcanic episode took place. Robert Griggs, exploring the volcano's aftermath for the National Geographic Society in 1916, stared awestruck off Katmai Pass across the valley's roaring landscape riddled by thousands of steam vents. The Valley of Ten Thousand Smokes, Griggs named. it.

Novarupta, Alaska, 1912: Largest eruption of the 20th century; produced 21 cubic kilometers (5 cubic miles) of volcanic material, which is equivalent to 230 years of eruption at Kilauea, Hawaii. Pyroclastic flow filled the Valley of Ten Thousand Smokes, and as much as 0.3 meter (1 foot) of ash fell 161 kilometers (100 miles) away.

The largest eruption in the world this century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6 -- about 30 times the volume erupted by Mount St. Helens in 1980! The expulsion of such a large volume of magma excavated a funnel-shaped vent 2 kilometers wide and triggered the collapse of Mount Katmai volcano 10 kilometers away to form a summit caldera 600 meters deep and about 3 kilometers across. Extrusion of the lava dome, called Novarupta near the center of the 1912 vent marked the end of the eruption.

Little was known about the spectacular effects of this great eruption until 1916, when a scientific expedition sponsored by the National Geographic Society visited the area. To their amazement, they found a broad valley northwest of Novarupta marked by a flat plain of loose, "sandy" ash material from which thousands of jets of steam were hissing. The eruption had produced pyroclastic flows that swept about 21 kilometers down the upper Ukak River valley. The thickness of the resulting pumice and ash deposits in the upper valley is not known but may be as great as 200 meters. In 1916, the deposits were still hot enough to boil water and form countless steaming fumaroles; hence the expedition named this part of the Ukak River the "Valley of Ten Thousand Smokes".

Novarupta was the source of the world's most voluminous 20th-century eruption, the most extensive historic ignimbrite, and of the only Quaternary high-silica rhyolite on the Alaska Peninsula. The 60-hour eruptive sequence of 6-8 June 1912 included (1) an initial rhyolite plinian fall with near-vent blasts, (2) an 11-cubic kilometer zoned ignimbrite sheet filling the Valley of Ten Thousand Smokes, and (3) a complex series of plinian dacite falls. Total ejecta volume was 30-35 cubic kilometers; magma volume was 12-15 cubic kilometers. The ignimbrite vent is marked by a 2-kilometer-wide backfilled depression, near the middle of which is nested the 500-meter-wide vent of the post-ignimbrite plinian dacite eruptions. A blocky rhyolite lava dome (Novarupta) subsequently plugged the inner vent.

Three discrete magmas erupted together, in part mingling syneruptively to yield an abundance of banded pumice: Quartz-hypersthene rhyolite (77.0% SiO2), pyroxene dacite (64.5-66% SiO2), and black pyroxene andesite (58.5-61.5% SiO2). More than half was rhyolite. Because the three vented concurrently and repeatedly after eruptive pauses hours in duration, the compositional gaps between them are thought intrinsic to the reservoir, not merely effects of withdrawal dynamics. K2O contents are 1.3-1.4% at 60% SiO2, 1.8-1.9% at 65%, and 3.2% at 77%. Major element variation trends are nearly identical to those of Mount Katmai and Trident. Linear fractures between Novarupta and Trident strike perpendicular to the volcanic front, raising the possibility that some or all of the 1912 magma was transferred to the 1912 vent from reservoir components beneath Trident; these, in turn, may have withdrawn magma from beneath Mount Katmai, permitting its collapse.

The "ten thousand smokes" in the ash-flow sheet mostly died out by 1930, and the few fumaroles remaining today are odorless wisps that issue from Novarupta and from intravent fractures nearby. Although orifice temperatures were as high as 645 degrees C in 1919, none are hotter than 90 degrees C at present. Many fossil fumaroles deposits, both pipelike and fissure-controlled, retain spectacular zoning in color, minerology, and composition.

[Image,64K,JPG]
Aerial view, Novarupta Dome, Katmai, Alaska.
-- USGS Photo by Gene Iwatsubo, July 29, 1987

Novarupta Volcano
Elevation: 841 meters
Relief: 70 meters
Volcano Diameter: 395 meters

The largest eruption in the world this century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6 -- about 30 times the volume erupted by Mount St. Helens in 1980! The expulsion of such a large volume of magma excavated a funnel-shaped vent 2 kilometers wide and triggered the collapse of Mount Katmai volcano 10 kilometers away to form a summit caldera 600 meters deep and about 3 kilometers across. Extrusion of the lava dome, called Novarupta, near the center of the 1912 vent marked the end of the eruption. ... The dome is 380 meters in diameter and occupies a small part of the vent from which about 15 cubic kilometers of magma was erupted ...

The nearly circular Novarupta Dome that formed during the 1912 eruption of Katmai Volcano, Alaska, measures 800 feet across and 200 feet high. The internal structure of this dome -- defined by layering of lava fanning upward and outward from the center -- indicates that it grew largely by expansion from within.

Novarupta was the source of the world's most voluminous 20th-century eruption, the most extensive historic ignimbrite, and of the only Quaternary high-silica rhyolite on the Alaska Peninsula. The 60-hour eruptive sequence of 6-8 June 1912 included (1) an initial rhyolite plinian fall with near-vent blasts, (2) an 11-cubic kilometer zoned ignimbrite sheet filling the Valley of Ten Thousand Smokes, and (3) a complex series of plinian dacite falls. Total ejecta volume was 30-35 cubic kilometers; magma volume was 12-15 cubic kilometers. The ignimbrite vent is marked by a 2-kilometer-wide backfilled depression, near the middle of which is nested the 500-meter-wide vent of the post-ignimbrite plinian dacite eruptions. A blocky rhyolite lava dome (Novarupta) subsequently plugged the inner vent.

[Map,30K,InlineGIF]
Location map for Novarupta and the Valley of Ten Thousand Smokes, Katmai National Park, Alaska, showing the 120-cubic-kilometer extent of the 1912 ash-flow sheet.
-- Modified from: Hildreth, 1983, IN: JVGR, v.18

The largest eruption in the world this century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6 -- about 30 times the volume erupted by Mount St. Helens in 1980!

Little was known about the spectacular effects of this great eruption until 1916, when a scientific expedition sponsored by the National Geographic Society visited the area. To their amazement, they found a broad valley northwest of Novarupta marked by a flat plain of loose, "sandy" ash material from which thousands of jets of steam were hissing. The eruption had produced pyroclastic flows that swept about 21 kilometers down the upper Ukak River valley. The thickness of the resulting pumice and ash deposits in the upper valley is not known but may be as great as 200 meters. In 1916, the deposits were still hot enough to boil water and form countless steaming fumaroles; hence the expedition named this part of the Ukak River the "Valley of Ten Thousand Smokes".

Few historic eruptions have been as provocative for petrologists and volcanologists as that of 1912 in the Valley of Ten Thousand Smokes at the northwest foot of Mount Katmai on the Alaska Peninsula. Among historic eruptions it is virtually unique in having generated a large volume of pumiceous pyroclastic flows that (unlike those of Krakatau and Santorini) came to rest on land. It was the century's most voluminous eruption by far, one of the three largest in recorded history, and one of the few historic eruptions to have produced welded tuff. An abundance of compositionally banded pumice evoked petrologic controversy, and the high-temperature fumaroles in the ash-flow sheet, which persisted vigorously for about 15 years, attracted attention to the vapor transport of metals (Allen and Zies, 1923; Zies, 1929).

The "ten thousand smokes" in the ash-flow sheet mostly died out by 1930, and the few fumaroles remaining today are odorless wisps that issue from Novarupta and from intravent fractures nearby. Although orifice temperatures were as high as 645 degrees C in 1919, none are hotter than 90 degrees C at present. Many fossil fumaroles deposits, both pipelike and fissure-controlled, retain spectacular zoning in color, minerology, and composition.

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