How Magma Reaches the Surface Magma forms in

How Magma Reaches the Surface Ø Magma forms in the (asthenosphere) mantle. Ø Magma is less dense than solid material so it rises toward the surface. Ø When a volcano erupts, dissolved gases form bubbles that rush out, taking the magma with them (like opening a can of soda pop) Ø the magma with them. Like When a volcano Reaches Earths Surface

Inside a Volcano ü ü ü Pipe: a long tube in the ground that connects the chamber to the Earth’s surface. Vent: where magma, and gas leave the volcano. Lava flow: the river of lava that comes out and over the land. Lava: Magma that reaches the surface is called lava. Crater: a bowl-shaped area that forms around the vent. Magma chamber: collects in pockets beneath the volcano.

Characteristics of Magma § The force of an eruption depends on four things…… § § § Silica also determines how easily the magma flows. More silica = thicker and lighter colored lava = sticky § § Amount of gas in magma How thick or thin the magma is Its temperature Silica content Makes obsidian and Rhyolite and pumice Less Silica = darker colored lava + flows easily § Makes basalt

Types of Volcanic Eruptions Quiet Eruptions Ø Magma is thin and flows easily Ø Pahoehoe: is a fast-moving hot lava, mass of wrinkles, billows and ropelike coils when it hardens. Ø AA: is a slow moving cool lava, rough and jagged when it hardens Ø Ø Explosive Eruptions- thick magma, pipe gets plugged and explodes when pressure builds up. Ø Causes pyroclastic flow explosive eruption hurls out gas, ash (sand-like), cinders (pebble sized), and bombs (larger pieces, ranging from baseball to car sized).

Stages of a Volcano Active or live volcano that is erupting or shows signs that it erupt in the near future. 2. Dormant or sleeping – scientists expect the volcano to erupt in the future and become active. 3. Extinct or dead is unlikely to erupt again. 1.

Volcanic Landforms

Landforms from Lava & Ash A. Shield Volcanoes B. Cinder Cone Volcanoes C. Composite Volcanoes D. Lava Plateaus E. Calderas

Shield Volcanoes Thin layers of lava pour out of a vent and harden on top of previous layers. Ø Build a wide, gently sloping mountain. Ø Hawaiian Islands are shield volcanoes over a hot spot. Ø

Mauna Loa, Hawaii

Cinder Cone Volcanoes A steep, cone-shaped hill or mountain. Ø Ash, cinders, and bombs pile up around the vent. Ø Cinders erupt explosively. Ø Sunset crater is an example. Ø

Composite Volcanoes A steep, cone-shaped volcano built up of layers and of rock fragments. Ø Steep at the top, flatens at the bottom Ø Magma- high in silica, making it pasty. Ø Erupt explosively. Ø Mount St. Helens and Mount Rainier are examples. Ø

Ø St. Augustine volcano, Alaska.

Lava Plateaus Continued eruptions form high, level areas. Ø Lava flows out of several long cracks, and after millions of years, these layers form high plateaus. Ø Example: Columbia Plateau Ø

Columbia Plateau

Calderas Ø A huge eruption may empty the main vent and the magma chamber beneath the volcano. Ø Mountain becomes a hollow shell and the top collapses in. Ø Huge hole left is called a caldera. Ø Example: Crater Lake, Oregon

Ø Poas Volcano, Costa Rica Ø Crater Lake, Oregon

Volcano Hazards q Mount St. Helens erupted in 1980 after 123 years of being dormant. Before that people viewed it as a peaceful mountain. q Quiet eruption hazards- lava flows from vents, burning everything in their path. q Explosive eruption hazards- volcano will send out burning clouds of volcanic gases, cinders and bombs. q Volcanic ash can bury entire towns, damage crops and clog car engines. Wet ash can cause roofs to collapse and plane engines to stall.