09 Ballistic Blocks and Other Hazards of Eruptions in the Lake

Volcano and Earthquake Hazards in the Crater Lake Region, Oregon

 Potential Hazards From an Eruption Beneath Crater Lake

Ballistic Blocks and Other Hazards of Eruptions in the Lake

A somewhat less serious hazard is the ejection of large ballistic blocks, tens of centimeters or more in diameter, to distances up to a few kilometers. Blocks have been ejected from hydromagmatic craters at velocities ranging from less than 100 m/s to nearly 250 m/s (Self and others, 1980; Lorenz, 1970). At Crater Lake, blocks ejected at these velocities could travel 1 to 4 km, and could easily overtop the caldera rim if the eruption vent were near the lake shore.

Other hazards include the development of water waves (seiches) during large explosions. Seiches at least a few meters in height accompanied the 1965 eruption of Taal volcano in the Philippines. Also, during an explosive eruption, surges might melt snow, or lake water might be ejected in sufficient volume, to mobilize surface debris and create lahars (volcanic debris flows) on the flanks of Mount Mazama (lahars are discussed below).

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