Oregon’s Pumice Desert

August 15, 2013

Take 3b

Photographer: Rebecca Roush
Summary Author: Rebecca Roush

The Pumice Desert shown above can easily be seen on Crater Lake Highway about 3.5 mi (5.6 km) north of the lake as the crow flies. This geologic feature, like Crater Lake itself, is the result of the massive eruptions of Mount Mazama approximately 7,700 years ago. When driving past the Pumice Desert, it’s hard to comprehend the depth of the pumice, which can reach more than 100 ft (30 m). Because this desert has so little organic matter, the landscape only occasionally provides enough nutrients for plant life. As a result, the soil has never been ameliorated by composting organic matter. The Pumice Desert forms a shallow basin, which implies that a deep valley may have been present prior to Mount Mazama’s eruptions. With a thick cover of ejecta, the original flows probably moved across the valley so quickly and with such strength that the basic basin-shape remained as the flows continued over the divide toward the north. Photo taken October 19, 2012.