Examples of Simultaneous Volcanic Eruptions


Novarupta vent and Mt. Katmai, Alaska: 1912

The largest eruption in the world this century at Novarupta vent on the Alasksa Peninsula ejected an estimated 15 cubic kilometers during a 60-hour period beginning June 6, 1912. So much molten rock was evacuated from magma reservoirs beneath the area that the summit of Mt. Katmai, 10 kilometers away, collapsed sometime during the eruption to form a caldera about 600 meters deep and 3 kilometers across! All of the magma erupted during the explosive eruption originated at the Novarupta vent, which is nearly surrounded by five volcanoes with active fumaroles and a history of eruptions in the past 10,000 years. Scientists have concluded that the magma systems beneath each of these volcanoes are sufficiently close together that the large withdrawal of magma from the Novarupta vent led to the transfer of magma below ground, probably by the structural failure of rocks between adjacent reservoirs. This underground movement of magma withdrew support from beneath Mt. Katmai, causing its summit to collapse.


Karymsky Volcano, Kamchatka Peninsula, Russia: 1996

The summary below is based on preliminary reports from the Smithsonian Institution Bulletin of the Global Volcanism Network that are subject to change.

By the time volcanologists had arrived by helicopter at Karymksy Volcano on January 2, 1996, less than 24 hours after a series of strong earthquakes had occurred within about 25 kilometers of the volcano, two volcanic vents from two overlapping calderas were erupting. Karymsky Volcano was erupting a small plume of ash from a vent only 50 meters below its summit. About 5 kilometers to the south, a much larger plume of ash (about 8 kilometers above sea level) was erupting from Karymsky Lake; ice that had covered the lake was completely melted. Within 2 weeks, a small lava flow was erupted from a second vent on Karymsky Volcano.

Karymsky Volcano is a stratovolcano located in the center of Karymsky Caldera, which formed about 7,800 years ago. The volcano is one of the most active on the Kamchatkan Peninsula; most of the cone is mantled with lava less than 200 years old. Karymsky Lake, however, is located at the north end of an adjacent caldera, the Akademia Nauk Caldera; there is no record of historic eruptions from this caldera. Both calderas are part of the Karymsky Volcanic Center which covers an area 50 x 35 kilometers.

For a preliminary summary of the initial eruptions from both vents, see the March 1996 Bulletin of the Global Volcanism Network.

For photos and a map of the two erupting vents, see the May 1996 Bulletin of the Global Volcanism Network.


Rabaul caldera, Papua New Guinea: 1994

Following the pattern of the last two eruptive episodes from Rabaul Caldera in 1878 and 1937- 43, there were almost simultaneous eruptions on opposite sides of the caldera on September 18, 1994. The eruptions occurred from two cones inside the caldera, Tavurvur and Vulcan. Tavurvur began erupting at 6:05 a.m. and Vulcan began erupting at 7:17 a.m. The eruption at Vulcan was the more powerful of the two.

Rabaul Caldera forms a sheltered harbor whose north end is occupied by Rabaul Town. Beginning as early as 1971 and increasing in 1983, a long period of unrest beneath the caldera (earthquakes and ground deformation) alerted scientists and residents alike of the possibility of renewed eruptive activity.


Kilauea & Mauna Loa volcanoes, Hawaii: 1984

Kilauea and Mauna Loa erupted simultaneously for 2 days in late March 1984, but there is no evidence to suggest that activity at one volcano caused the eruption of the other volcano. Mauna Loa began erupting on March 25 from its summit caldera and within a few hours, the eruption site had shifted to its northeast rift zone. After erupting 220 million cubic meters of lava and threatening the city of Hilo, the eruption ended on April 15. Kilauea Volcano had actually started erupting more than a year earlier in January 1983, but the eruption consisted of intermittent episodes of high lava fountains every few weeks from the Pu'u O'o vent. Episode #17 occurred March 30-31, and the activity was no different from episodes that occurred just before or after the Mauna Loa eruption.