Chapter 9 Section 2 Volcanoes

Effects of Volcanic Eruptions In 1816, Chauncey Jerome, a resident of Connecticut, wrote that the clothes his wife had laid out to dry the day before had frozen during the night. This event would not have been unusual except that the date was June 10!

What You Will Learn Explain how volcanic eruptions can affect climate. Compare the three types of volcanoes. Compare craters, calderas, and lava plateaus.

Volcanic Eruptions and Climate Change The explosion of Mount Tambora in 1815 blanketed most of Indonesia in darkness for three days. It is estimated that 12,000 people died directly from the explosion and 80,000 people died from the resulting hunger and disease.

Volcanic Eruptions and Climate Change (continued) As volcanic ash and gases spread throughout the atmosphere, they can block enough sunlight to cause global temperatures to drop. The Tambora eruption affected the global climate enough to cause food shortages in North America and Europe. More recently, the eruption of Mount Pinatubo, shown in Figure 1, caused average global temperatures to drop by as much as 0.5°C.

Mount Pinatubo

Different Types of Volcanoes Volcanic eruptions can cause profound changes in climate. But the changes to Earth’s surface caused by eruptions are probably more familiar. Perhaps the best known of all volcanic landforms are the volcanoes themselves.

Shield Volcanoes Shield volcanoes are built of layers of lava released from repeated nonexplosive eruptions. Because the lava is very runny, it spreads out over a wide area. Over time, the layers of lava create a volcano that has gently sloping sides. Although their sides are not very steep, shield volcanoes can be enormous. Hawaii’s Mauna Kea is taller than Mt. Everest

Cinder Cone Volcanoes Cinder cone volcanoes are made of pyroclastic material usually produced from moderately explosive eruptions. The pyroclastic material forms steep slopes Cinder cones are small and usually erupt for only a short time. Cinder cones often occur in clusters, commonly on the sides of other volcanoes. They usually erode quickly because the pyroclastic material is not cemented together.

Composite Volcanoes Composite volcanoes, sometimes called stratovolcanoes, are one of the most common types of volcanoes. They form from explosive eruptions of pyroclastic material followed by quieter flows of lava. The combination of both types of eruptions forms alternating layers of pyroclastic material and lava. Composite volcanoes in the western region of the United States include Mount Hood, Mount Rainier, Mount Shasta, and Mount St. Helens.

Other Types of Volcanic Landforms In addition to volcanoes, other landforms are produced by volcanic activity. These landforms include craters, calderas, and lava plateaus.

Craters Around the central vent at the top of many volcanoes is a funnel-shaped pit called a crater. An example of a crater is shown in Figure 3. During less explosive eruptions, lava flows and pyroclastic material can pile up around the vent creating a cone with a central crater. As the eruption stops, the lava that is left in the crater often drains back underground.

Calderas Calderas can appear similar to craters, but they are many times larger. A caldera is a large, semicircular depression that forms when the chamber that supplies magma to a volcano partially empties and the chamber’s roof collapses. As a result, the ground above the magma chamber sinks, as shown in Figure 4. Much of Yellowstone Park is made up of three large calderas that formed when volcanoes collapsed between 1.9 million and 0.6 million years ago. Today, hot springs, such as Old Faithful, are heated by the thermal energy left over from those events.

Lava Plateaus The most massive outpourings of lava do not come from individual volcanoes. Most of the lava on Earth’s surface erupted from long cracks, or rifts, in the crust. In this type of eruption, runny lava can pour out for millions of years and spread over huge areas. A landform that results from repeated eruptions of lava spread over a large area is called a lava plateau.

Section Summary The large volumes of gas and ash released from volcanic eruptions can affect climate. Shield volcanoes result from many eruptions of relatively runny lava. Cinder cone volcanoes result from mildly explosive eruptions of pyroclastic material. Composite volcanoes result from alternating explosive and nonexplosive eruptions. Craters, calderas, and lava plateaus are volcanic landforms.