Betweem 1980 and 1986, Mount St. Helens' dome grew in different ways. From 1980 through 1982 the dome grew in periodic extrusions of stubby lava flows, called lobes. This pattern changed in February 1983, when growth became continuous and mostly endogenous (internal). Perioidic lobe growth, along with endogenous growth, resumed in early 1984. Pictured here is an aerial view of Mount St. Helens' dome and the June 1981 lobe with its "spreading center". A spreading center is the area from which new lava slowly emerges during lobe growth. During this time frame Mount St. Helens' lobes grew at a rate of 3 to 10 feet per hour (1-3 meters/hour).
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Photo credit: © CPC Collection / Alamy / Afripics
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