Volcanic Eruptions

1. Volcanic Eruptions Pgs. 148 - 152

2. Eruptions • How big can an eruption be? • 10,000 times as big as an atomic bomb. • Where do eruptions come from? • Volcanoes • Volcano – mountain that forms when molten rock called magma is forced to the Earth’s surface. • Eruptions can be either explosive or nonexplosive. • Most are nonexplosive.

3. Nonexplosive Eruptions • Lava, magma that flows onto the Earth’s surface, is what results from a nonexplosive eruption. • Volcanoes with nonexplosive eruptions will calmly pour out lava. • Lava is typically not fast moving, but can be very destructive. • Sometimes pressure can build up where the lava comes out and it might spray into the air and form a lava fountain.

4. Explosive Eruptions • In explosive eruptions, clouds of hot debris and gases shoot out from the volcano at incredible speeds. • Instead of lava, magma spews into the air in millions of pieces and cools quickly. • Small pieces will travel in the air and spread while larger pieces are thrown to the ground around the volcano. • Sides of the volcano can even get blown out. • The size of the volcano will actually shrink if the explosion is violent enough.

5. Volcano Cross Section • All volcanoes share similar basic features regardless of explosive or nonexplosive eruptions. • All of them have a magma chamber at the base underneath the Earth. • Magma can rise through vents, holes in the Earth’s crust between the Earth’s surface and the magma chamber.

6. Magma • The composition of magma can vary. • The composition also determines if a volcano is explosive or not. • High water content is characteristic of an explosive eruption. • It is similar to carbon dioxide in a can of soda. • Shake it and the pressure builds up. • The soda shoots out of the can when it is opened.

7. Silica in Magma • A high silica content in magma is characteristic of explosive magma. • Silica is mostly silicon and makes magma stiff and thick. • It will make magma slow and it can clog vents. • When vents are clogged, they trap gases in the magma chamber and pressure builds up and eventually blows. • Low silica magma is thinner and runnier in consistency. • Gases are able to escape much easier.

8. When a Volcano Erupts • Depending upon the explosive capability of the magma in the volcano, it will expel either lava or pyroclastic flow. • Lava is molten rock that flows slowly on the Earth’s surface. • Pyroclastic material is rock fragments created by explosive eruptions. • Magma from within the volcano explodes into the air and solidifies quickly.

9. Lava • Since magma can range in consistency, so can lava. • Blocky lava • Thick in consistency; barely moves; and forms heaps of sharp edged chunks. • Pahoehoe • Thinner consistency; similar to candle wax; it forms a glassy surface with ripples when solid. • Pillow lava • Forms when lava erupts underwater and forms lumps the size and shape of pillows. • AaAa • Lava that has formed a jagged surface

10. Pyroclastic Material • Pyroclastic material can range in a variety of sizes and shapes • Volcanic blocks • Solid rock blasted out of the volcanoes. • Volcanic bombs • Large blobs of magma that harden in the air in the shape of a bomb. • Lapilli • “little stones” pebble-like bits of magma that became solid before they hit the ground. • Volcanic ash • Forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny glasslike slivers