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Ash and Tephra from Medicine Lake Volcano

Tephra and gases from eruptions are carried away from the vent by prevailing winds. Tephra accompanying silicic eruptions could be regionally widespread if the eruption column rises several kilometers into the air, as would be likely. At Medicine Lake Volcano the fallout could cause short-term disruption of activities in Klamath Falls if the wind direction took volcanic ash to the north. Local communities, Lava Beds National Monument, roads and highways, and the utility corridor that crosses the east and south sides of the volcano would probably be affected for days or weeks.

Mafic eruptions are much less likely to produce large volumes of tephra than silicic eruptions. Numerous basalt to andesite cinder cones at Medicine Lake volcano indicate explosive activity at these vents, and the associated eruption columns may have risen several kilometers into the atmosphere. Close to the vents, volcanic bombs and scoria are deposited to form the cones, but such deposits typically thin quickly away from the vents. Therefore, tephra and ash from these eruptions may only be deposited up to a few kilometers away.

If a volcanic vent were to open under Medicine Lake, the eruption would almost certainly be accompanied by phreatomagmatic eruptions that would deposit wet, muddy tephra over the immediate area, including the campgrounds and cabins, and perhaps over much of the caldera. If magma intruded into the shallow hydrothermal system, which has been identified beneath the caldera by geothermal exploration drilling, phreatic (steam) eruptions might occur at the surface. These are also known as hydrothermal explosions.

At Medicine Lake Volcano, there is a 1 in 5,000 chance of an eruption producing enough tephra to accumulate to 1 cm (0.4 in) thick in any given year. Although 1 cm of ash may seem a very small amount, experience with Mount St. Helens eruptions indicates that as little as 0.5 cm (0.2 in) of ash is sufficient to slow vehicle traffic to a crawl and to close businesses for as much as a week or two. Near-vent accumulations of tephra could be many meters thick (1 m = 3.2 ft), but no permanent habitations exist at Medicine Lake volcano close to likely silicic vent locations. Aircraft could be affected by any eruption that generates tephra that rises high enough into the atmosphere to disrupt an airplane's path.