Katmai volcano was incorrectly thought to be the source of the largest eruption of the 20th Century. The great eruption began on June 6, 1912 after large earthquakes shook the region on the previous two days. The area was so remote that it was four years before Robert Griggs led an expedition to investigate the eruption. The expedition was funded by the National Geographic Society.
Katmai summit with lake in the caldera, USGS
Little known about Katmai before the eruption
Prior to the great eruption the volcano was a little known 7,500 ft peak in Alaska. The expedition studying the eruption found that the volcano was drastically altered after the event.
Summit collapsed during eruption
The summit of the volcano had collapsed when magma drained out of the volcano during the eruption. The summit's collapse formed a two mile wide caldera that had started to fill with water from melting snow.
New dome named Novarupta
The expedition found a valley filled with pyroclastic material from pyroclastic flows that covered 40 square miles and a small dome a short distance from Katmai volcano.The expedition named the dome Novarupta.
40 years source of eruption was Katmai volcano
Griggs was sure that Katmai was the source of the eruption because of the summit collapse on Katmai volcano. During the next forty years textbooks attributed the great eruption to Katmai.
Katmai National Monument created
Griggs was so impressed with his findings that he persuaded President Woodrow Wilson to create Katmai National Monument in 1918. Today the area is a national park where visitors can visit the volcanoes in the area and watch bears feed on salmon as they come up the streams in the summer and fall.
1950s Novarupta source eruption
Scientists studying the eruption in the 1950s discovered that Novarupta Volcano was the source of the all the pyroclastic material. The only new magma that flowed out of Katmai during the eruption formed a small dome.
Horseshoe Island Dome
The small dome was named Horseshoe Island. Horseshoe Island was visible when Griggs's party studied the summit of the Katmai. Today the island is covered with water. The lake in the caldera is now 800 feet deep. Small glaciers have also formed on the slopes of the snow covered peak
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