In the past, drum recorders were used to display seismograms on pieces of paper. These mechanical records have largely been replaced by computers, which digitize the data and store it in digital form. The digital data can be displayed in a variety of ways by a computer, such as a webicorder plot. This webicorder video provides a tutorial for anyone interested in interpreting the seismic records on public webicorder displays.
In the early morning hours of September 23, 2004, a swarm of small-magnitude earthquakes about half a mile below Earth's surface marked the reawakening of Mount St. Helens. On October 1, 2004, the first of several small explosions shot a plume of volcanic ash and gases skyward. A growing welt beneath Crater Glacier heralded the rise of semi-solid magma that erupted onto the surface, forming rocky spines, smooth-sided ridges, and jumbled piles of lava over the next 34 months. During the eruption, scientists made important strides in volcano monitoring, developing new tools for investigation and insight into eruptive behavior. View the 2004-2008 Mount St. Helens Eruption video and read about the eruption in the 2004-2008 event timeline and statistics.