100 years ago, the largest volcanic eruption of the 20^th century occurred on the Alaska Peninsula, west of Anchorage. Beginning on June 6th, 1912, a new vent produced an explosive three day eruption that produced 13.5 cubic kilometers of material (over 3 times larger than the 4 cubic kilometers of the 1980 of Mount St Helens!). Pyroclastic flows filled and flattened the upper reaches of the Illiuk Arm of the Naknek drainage with hot ash, pumice, and older rocks forming a 150-meter thick ignimbrite deposit. The ignimbrite emitted steam from thousands of fumaroles (steam vents) for many years, which gave the valleys its name, the Valley of 10,000 Smokes. 

As the eruption waned, the viscous magma, now devoid of volatile gases, created a blocky lava plug and dome directly above the vent.  This new vent and dome are now known as Novarupta.

Directly following the eruption, the nearby Katmai composite volcano, 10 km to the east, suddenly collapsed and formed a 1 km deep caldera. This caldera subsequently filled with a crater lake over 240 meters deep.

Katmai National Park is a spectacular, rugged place that is geologically overwhelming. A deep, narrow canyon has been carved by seasonal snowmelt into the 150-meter ignimbrite deposit. The Katmai Caldera is now filled with deep blue glacial water. The Valley of 10,000 smokes has stopped smoking but still illustrates the immense amount of material ejected from Novarupta 100 years ago. The Novarupta dome stands separate from the nearby cluster of composite volcanic cones as evidence of the unpredictability of volcanic processes.