affected by light ashfalls similar to those it experienced during the 1980 eruptions of Mount St. Helens. The city will not be directly affected by lava flows, pyroclastic flows, or lahars, but regional transportation and water supplies could be disrupted. (Photo by David Wieprecht, USGS).Mount Hood is more than 500,000 years old. The volcano has grown in fits and starts, with decades to centuries of frequent eruptions separated by quiet periods lasting from centuries to more than 10,000 years. In the recent past, Mount Hood has had two significant eruptive periods, one about 1,500 years ago and the other about 200 years ago.
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