10 Proximal Hazard Zones for Explosive Eruptions

Volcano and Earthquake Hazards in the Crater Lake Region, Oregon

 Potential Hazards From an Eruption Beneath Crater Lake

Proximal Hazard Zones for Explosive Eruptions

The type of volcanic eruption considered most likely at Crater Lake would take place from a vent within the caldera, probably beneath the surface of the lake. We have defined Proximal Hazard Zone PA as the caldera itself, bounded by the caldera rim (plate 1). Proximal Hazard Zone PB is the maximum area we judge likely to be affected by pyroclastic surges and ballistic ejecta, assuming an eruption that breaks the surface of the lake.

The outer boundary of Proximal Hazard Zone PB was drawn by assuming a maximum height of ejection of surge-forming material of 500 m above the lake surface and a ratio of height of drop to runout distance of 1:10, or H/L = 0.1, for vents within the lake and close to the shoreline (such a low ratio maximizes predicted runout). Surges would be funneled through low areas on the caldera rim and channeled into valleys. Although surges would not be expected on the higher ground, we have included the entire area within 1.5 km of the rim within zone PB because of a possible hazard from exceptionally energetic ballistic blocks. For the same conditions of height of origin, surges from vents near the center of the lake would not surmount the caldera walls and ballistics would fall within the caldera. Crater Lake Lodge, Rim Village, and structures in the park headquarters area are at highest risk from an eruption in the southwest quadrant of the lake. An eruption elsewhere in the caldera might not affect this area with pyroclastic surges but might result in tephra fall there if wind conditions were appropriate.

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