Works in Progress: Birth of a Volcano

The 10,000-foot peaks in western Oregon known as the Three Sisters were once a flat stretch of real estate. Then the ground began to tremble and bulge, and the first in a long series of volcanic eruptions spewed ash and debris as far south as California and out into the Pacific Ocean. Such eruptions have been building the Sisters from lava and cinders for about 700,000 years. The last one occurred 2,000 years ago, at South Sister; it's been pretty quiet ever since.