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Area around Crater Lake, Oregon. This is called a Pumice Desert, and the pumice deposits shown are the product of Mt. Mazama, and explosive volcano that collapsed to form the Crater Lake caldera. Mazama stood about 6 miles south of here. About 7,700 years ago, Mt. Mazama erupted torrents of seething, red-hot pumice and other volcanic rocks. These glowing avalanches raced down the slopes and flooded the valley that lay here with deposits over 100 feet deep. Even after thousands of years, few trees have become established on the Pumice Desert. There is ample water under the surface, but deficiencies in the soil limit plant growth. Many more years will pass before the surrounding lodgepole pines transform the desert to a forest. (09/28/2004)