Primary Succession & Species Diversity of Flora on Mount St. Helens, 32 Years Post-Eruption
Geoff Hibbs May 4, 2012 Primary Succession & Species Diversity of Flora on Mount St. Helens, 32 Years PostEruption On May 18 1980, Mount St. Helens, a stratovolcano in western Washington, erupted. The eruption scoured the slopes of the volcano removing vegetation and soil from the vicinity of the mountain. 32 years after the eruption, vegetation has returned to the mountain. The author’s main interest in this field is the methods by which vascular plants re-establish themselves after cataclysmic, soil-removing volcanic eruptions, and if some plants are better suited than others to re-establishing on volcanic tephra and other eruptive debris. The author believes that it is important to understand how volcanism affects succession and diversity patterns, due to the ongoing activity of Mount St. Helens, and the potential for eruptive activity from the other mountains of the Cascade volcanic arc in the future. In order to understand the processes leading to the current species diversity of Mount St. Helens, one must understand the disturbance that prefaced vegetation establishment. According to Tilling, Topinka, and Swanson of the United States Geological Survey, the 1980 eruption of Mount St. Helens was the most significant volcanic event in the United States since the eruption of Lassen Peak in California in 1915. The mountain’s eruptive activity began in early March of 1980, with a series of
minor earthquakes and small eruptions. This period lasted until May 18, when the weakened northern slope of the volcano was shaken by a large earthquake, and collapsed in a massive landslide. The slide itself covered roughly 24 square miles of the terrain north of Mount St. Helens in material up to 150 feet thick (Tilling, Topinka, and Swanson). Behind the slide, a lateral volcanic blast, released from the pressure of the overlying rock, traveled at speeds of up to 700 miles per hour in a fan-shaped flow northwards from the mountain. This blast, ejecting 208 million cubic
minor earthquakes and small eruptions. This period lasted until May 18, when the weakened northern slope of the volcano was shaken by a large earthquake, and collapsed in a massive landslide. The slide itself covered roughly 24 square miles of the terrain north of Mount St. Helens in material up to 150 feet thick (Tilling, Topinka, and Swanson). Behind the slide, a lateral volcanic blast, released from the pressure of the overlying rock, traveled at speeds of up to 700 miles per hour in a fan-shaped flow northwards from the mountain. This blast, ejecting 208 million cubic