before becoming extinct. The rest are polygenetic shield volcanoes. About 80 percent of the lava erupted by Indian Heaven volcanoes consists of basalt; it represents the most voluminous Quaternary basalt produced by a volcanic field in the Cascade Arc north of Newberry Volcano in Oregon, with an eruptive output volume between . Basalt composition varies from low-potassium high-alumina olivine tholeiite to calc-alkaline, shoshonite, and alkaline intraplate compositions, though olivine-bearing basalt with different amounts of porphyritic plagioclase dominates. Volcanoes within the field have produced smaller amounts of basaltic andesite and andesite with silicon dioxide compositions up to 59 percent, though dacite is not very common among Indian Heaven eruptive products. Unlike Mount St. Helens, the Indian Heaven field has generated large volumes of basalt but has not caused extensive crustal melting. Most of the lava flows produced by the field have been pāhoehoe, featuring smaller percentages of block flows and ʻaʻā flows. They vary in thickness from , reaching volumes up to ; there are about 40 distinct lava flow groups in the field, totaling in area. Indian Heaven has been significantly altered through glacial erosion, including at least four major periods of glaciation. During the Hayden Creek Glaciation from 190,000 to 130,000 years ago, the Lewis River glacier advanced from Mount Adams to fill the Lewis River canyon, partly overlapping the Indian Heaven volcanic field. An ice cap originating at the northern end of the field also spread during this glacial era. The Lone Butte tuya volcano erupted through this glacier, which had a thickness of . Eruptive history and potential hazards One of Indian Heaven's vents produced a large effusive eruption about 9,000 years ago, forming the Big Lava Bed, which consisted of basaltic lava. With an area of and a volume of , the Big Lava Bed mostly consists of unvegetated basalt. It moved to the south down the Little White Salmon River drainage, which it filled for of its length. Ultimately, the flow extended from its initial source vent, an unnamed cinder cone. It came within of the Columbia River. Another, more ancient lava flow that was especially fluid encompassed the Trout Lake area and extended several miles south, also nearing the Columbia River. Highly voluminous, it also features lava tubes. These lava tubes can be found at many of the lava flows that comprise the Indian Heaven volcanic field, which range from basaltic to andesitic in