2 How Magma Reaches the Surface Magma forms in the (asthenosphere) mantle.Magma is less dense than solid material so it rises toward the surface.When a volcano erupts, dissolved gases form bubbles that rush out, taking the magma with them (like opening a can of soda pop)the magma with them. Like When a volcano Reaches Earths Surface
3 Inside a VolcanoPipe: 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.
4 Characteristics of Magma The force of an eruption depends on four things……Amount of gas in magmaHow thick or thin the magma isIts temperatureSilica contentSilica also determines how easily the magma flows.More silica = thicker and lighter colored lava = stickyMakes obsidian and Rhyolite and pumiceLess Silica = darker colored lava + flows easilyMakes basalt
5 Types of Volcanic Eruptions Quiet EruptionsMagma is thin and flows easilyPahoehoe: is a fast-moving hot lava, mass of wrinkles, billows and ropelike coils when it hardens.AA: is a slow moving cool lava, rough and jagged when it hardensExplosive Eruptions- thick magma, pipe gets plugged and explodes when pressure builds up.Causes pyroclastic flow explosive eruption hurls out gas, ash (sand-like), cinders (pebble sized), and bombs (larger pieces, ranging from baseball to car sized).
6 Stages of a VolcanoActive or live volcano that is erupting or shows signs that it erupt in the near future.Dormant or sleeping – scientists expect the volcano to erupt in the future and become active.Extinct or dead is unlikely to erupt again.
11 Cinder Cone Volcanoes A steep, cone-shaped hill or mountain. Ash, cinders, and bombs pile up around the vent.Cinders erupt explosively.Sunset crater is an example.
12 Composite VolcanoesA steep, cone-shaped volcano built up of layers and of rock fragments.Steep at the top, flatens at the bottomMagma- high in silica, making it pasty.Erupt explosively.Mount St. Helens and Mount Rainier are examples.
16 CalderasA huge eruption may empty the main vent and the magma chamber beneath the volcano.Mountain becomes a hollow shell and the top collapses in.Huge hole left is called a caldera.Example: Crater Lake, Oregon
19 Volcano HazardsMount St. Helens erupted in 1980 after 123 years of being dormant. Before that people viewed it as a peaceful mountain.Quiet eruption hazards- lava flows from vents, burning everything in their path.Explosive eruption hazards- volcano will send out burning clouds of volcanic gases, cinders and bombs.Volcanic ash can bury entire towns, damage crops and clog car engines. Wet ash can cause roofs to collapse and plane engines to stall.