KATU-TV (Television Station : Portland, Or.)

Mount St. Helens, about 50 miles northeast of Portland, Oregon, is a composite volcano with a steep-sided, somewhat symmetrical cone made up of ash and lava in alternating layers. It has been active many times during the last two centuries, including a possible eruption in 1800, intermittent eruptions between 1831 and 1857, and possible minor eruptions in 1898, 1903, and 1921. The 1980 eruptions were the first major volcanic eruptions in the conterminous United States since Lassen Peak (Calif.) in 1914.

March and April 1980 were months of intense activity, including more than 10,000 earthquakes, hundreds of small steam explosions and the distension of the north side of the mountain. On May 18, a magnitude 5.1 earthquake triggered the largest landslide in recorded history on the north side of the volcano. The resulting eruption lasted 9 hours and sent ash over several states. The lateral blast leveled miles of forest, and mudflows devastated the Toutle River Valley.

From the guide to the Mount Saint Helens Eruption Moving Image Collection, March-May 1980, (Oregon Historical Society Research Library)