Eruptions from any volcano in the Three Sisters region, as well as from more distant volcanoes in the Cascade Range, are sources of potential tephra fall in Central Oregon communities.
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Since the last glacial maximum, the thickest tephra fall in the Bend, Oregon, area, probably about 30 cm (1 ft), originated from the huge eruption of Mount Mazama that created Crater Lake about 7,700 years ago. The most recent eruptions from South Sister produced tephra that fell more than 2 m thick (7 ft) within 2 km (1 mi) of the vent and deposited a coating of ash at locations as far as 40 km (25 mi) south and east of the vents (extending into Bend).