By Melissa Wynn
courtesy NPS.gov
Did you know that all four types of volcanoes on earth (Cinder Cone, Shield, Composite and Plug Dome) are represented in Lassen Nation Park?
Cinder cone volcanoes (Cinder Cone) are formed from explosive eruptions where materials spew high in the air and cool before they hit the ground. Fine-grained rocks are blown away by winds. Coarser rock fragments remain in a cone-shaped pile, which can be hundreds of meters tall.
Shield volcanoes (Prospect Peak) are formed by frequent, quiet eruptions and are much larger in width than in height. As smooth lava flows build up, a dome shape is formed. Shield volcanoes usually change shape when eruptions become explosive late in the life of the volcano.
Composite volcanoes (Brokeoff Volcano) are very large and are formed from alternating explosive eruptions and quiet eruptions. This results in layers of ejected material covered by smooth lava flows. Composite volcanoes are usually symmetrical in shape and can be as high as several kilometers.
“Lassen Peak (Plug Dome) is the largest of a group of more than 30 volcanic domes erupted over the past 300,000 years in Lassen Volcanic National Park in northern California. With a height of 2,000 feet and a volume of half a cubic mile, it is one of the largest lava domes on Earth”. — Excerpts from: Clynne, et.al., 1999, Eruptions of Lassen Peak, California, 1914 to 1917: USGS Fact Sheet 173-98
www.vulcan.wr.usgs.gov
