During June 6 to 9, 1912, the most spectacular Alaskan eruption in recorded history and the twentieth century's largest measured volcanic eruption formed a large summit caldera at Katmai volcano. The eruption happened at a vent about to the west of Mount Katmai (at the Novarupta Volcano). During over 60 hours, the volcano erupted an estimated of ash flows and tephra representing of magma volume. The eruption produced a cloud of suffocating gas and ash that blackened the sky for the inhabitants of the town of Kodiak, who, with ash falling on them were led to the U.S. Coast Guard Cutter Manning where they sheltered in the harbor and were cared for by the crew because Captain Perry determined "an attempt to leave here would be unwise" because the eruption made navigation dangerous. The withdrawal of magma beneath Katmai resulted in the collapse of the summit area, forming the caldera. Following the subsidence, a small dacitic lava dome known as Horseshoe Island was emplaced on the floor of the caldera; this is the only juvenile material erupted from Katmai caldera during the historical eruption. It was visible at the time of the expedition in 1916, but has since been submerged by the crater lake. Still, the eruption from Katmai had a VEI of 3, and possibly involved phreatic eruptions.