Volcanoes’ Effects on Earth

1. Volcanoes’ Effects on Earth Pgs. 153 - 155

2. Explosive Impact • Volcanic eruptions affect both the air and land. • Pyroclastic flow thrown into the air can knock down trees, buildings, and towns. • Ash ejected from eruptions can block out the sun for days over large areas.

3. Flows and Fallout • Clouds of ash can flow down mountains like avalanches. • The effects can be devastating. • Ash can dam up river valleys, producing massive floods. • It can destroy crops. • It can kill livestock. • Almost everything in its path will be destroyed.

4. Climatic Changes • In large scale eruptions, ash and sulfur-rich gases can reach the upper atmosphere. • The ash can block out the sun over vast areas, causing a dramatic drop in temperature for weeks or months. • The change will bring cooler summers with harsher winters. • The sulfur-rich gases can cause large amounts of acid rain as well.

5. Volcanoes • Volcanic eruptions eject lava and pyroclastic flow that actually help create a variety of landforms. • The volcanoes themselves are a build up of rock around a vent. • The three major types of volcanoes are shield, cinder cone, and composite.

6. Shield Volcano • Shield volcanoes are built out of layers of lava from repeated nonexplosive eruptions. • The lava spreads out over a period of time creating layers of gentle sloping sides. • The sides of a shield volcano are not steep, but can be extremely large. • Mauna Kea, in Hawaii, is a shield volcano starting from the ocean floor. • It measures higher than Mt. Everest.

7. Cinder Cone Volcano • Cinder cones are small volcanic cones made entirely out of pyroclastic material. • It has steeper slopes and a narrower base than a shield volcano. • Cinder cones usually erupt for only a short time and often occur in clusters. • They erode quickly because the pyroclastic particles are not cemented together by lava.

8. Composite Volcano • Composite volcanoes form by explosive eruptions of pyroclastic material followed by quieter outpourings of lava. • They form alternating layers of material (pyroclastic and lava). • These are the most common type of volcano. • These volcanoes have broad bases, but get steeper toward the summit. • Mt. Fuji in Japan is a composite volcano.

9. Craters and Calderas • At the top of the central vent in most volcanoes is a funnel-shaped pit called a crater. • The funnel shape is a result from explosions of material out of the vent and collapse of material. • When a magma chamber that supplies material to a volcano empties and its roof collapses it is called a caldera. • The ground actually sinks, leaving a large circular depression. • Calderas are usually much larger than volcanic craters.

10. Lava Plateaus • Most of the lava on Earth’s continents erupts from long cracks, or fissures, in the crust. • Here lava pours out of many fissures and spreads evenly over thousands of square kilometers. • This large area is known as a lava plateau. • These outpourings of lava are the most massive ejections of lava material.