By September, seismic activity returned to normal and no more carbon dioxide was detected. There are many chapters still to be written in the story of Mount St. Helens. Some read like a quiet afternoon, while others tell the tale of awaiting disaster. Although the volcano has been relatively quiet since its last eruptive activity in 1991-92, natural forces continue to create changes in the landscape. In the summer months, rocks fall from the steep crater walls and sides of the lava dome, contributing to the mass of rock, snow and ice that fills the crater.
Water gradually carves new channels into the pumice plain.
Little by little these new drainages cut their way into the mountain toward the crater. Sometimes, however, processes which normally operate so slowly that we barely notice them can occur in the space of few moments. During September of 1997 heavy rains fell on the volcano. One of these rapidly flowing mixtures of water and rock up to 60 feet thick roared out of the crater and spilled onto the pumice plain below. Smaller lahars were also generated on the western flank of the volcano, damaging trails and roads and spilling sediment into Blue Lake.