VOLCANOES

Warm Up Imagine that it is about 5pm and you have just washed a load of clothes. Since it is June and very warm outside, you decide to dry the clothes on a clothesline. You forget to take the clothes back off of the line before going to bed that night, and when you wake up the next morning it is very cold outside and your clothes have frozen on the line. It is supposed to be Summer, so how has this happened? What has caused this dramatic shift in temperature? Speculate as to how this may have occurred and record your answer in complete sentences.

VOLCANOES A volcano is an opening in the Earth’s crust where magma occasionally exits. They are typically associated with Oceanic/Continental and Oceanic/Oceanic Convergent Boundaries but can also form due to Hotspots. Shield Volcanoes Cinder Cone Volcanoes Composite (Strato-) Volcanoes

SHIELD VOLCANOES Shield Volcanoes form when lava quickly pours out of a vent and accumulates around the vent. These are the biggest volcanoes. They are the least explosive type of volcano. They have very broad sides. Shield volcanoes can be found in Hawaii

CINDER CONE VOLCANOES They are the smallest type of volcano. Cinder Cone Volcanoes form when rock fragments shoot out of a volcano, fall back down, and accumulate around the vent. They are the smallest type of volcano. They are more dangerous than shield volcanoes. They have the steepest sides of any volcano.

COMPOSITE (STRATO-) VOLCANO Composite Volcanoes, also known as Strato-Volcanoes, form at convergent plate boundaries. A subducting plate melts rock and pushes magma through the crust to form a volcanic mountain. They are the most dangerous type of volcano. Many are located along the Pacific Ring of Fire. Mt. St. Helens is an example.

HOT SPOTS Hotspots are unusually hot regions of Earth’s mantle where magma occasionally rises to the surface and forms a volcano. The Hawaiian Islands were formed by the Pacific Plate moving over a hotspot. There is also a hotspot beneath Yellowstone Park.

MAGMA Magma is molten (melted) rock that is stored below Earth’s surface. Once magma reaches the Earth’s surface it is then known as lava.

MAGMA Viscosity – A liquid’s resistance to flow. Types of magma: The higher a liquid’s viscosity is, the slower it moves. High silica content equals high viscosity. Low silica content equals low viscosity. High viscosity magma produces greater volcanic explosions. Low viscosity magma produces little or no volcanic explosions. Types of magma: Rhyolitic – Most explosive Andesitic – Second most explosive Basaltic – Least explosive

The 3 Stages of Volcanic Activity Active: A volcano that is in the process of erupting. Dormant: A volcano that is not currently erupting, but may still have volcanic activity occurring under the surface. Extinct: A volcano that is not likely to ever erupt again due to declining or non-existent activity below the surface.

PYROCLASTIC FLOW AND ASH IN THE ATMOSPHERE Pyroclastic flows are violent volcanic eruptions that can send ash and rock fragments down a slope at incredible speeds. These flows are very hot and often contain poisonous gases. Ejected ash can block out the sun and cause climate shifts.

LAHAR A lahar is a mudflow caused by volcanic activity. Volcanic activity melts glaciers at the top of volcanoes. Water then rushes down the mountain picking up sediment and other material that is then carried down the slope.

MOUNT ST. HELENS Mount St. Helens is part of the Cascade Range which is part of the Pacific Ring of Fire. On May 18, 1980 Mt. St. Helens erupted. It was the deadliest eruption in the history of the US. Approximately 57 people killed. Over 250 Homes destroyed. Countless animals killed and habitat lost.