1. Ch.6, Sec.1 - Volcanic Eruptions
volcano: a vent or fissure in the Earth’s surface through which magma and gases are expelled
- molten rock in volcanoes is called magma & lava is molten rock on Earth’s surface -
Nonexplosive Eruptions
- these eruptions are the most common type and they produce calm flows of lava
Explosive Eruptions
- these eruptions are less common and blow dust-size ash particles into the atmosphere with millions of tons of lava

2. Ch.6, Sec.1 - Volcanic Eruptions
Mount St. Helens before the eruption of May 18, 1980
Mount St. Helens 30 years after the eruption in May, 2010

3. Ch.6, Sec.1 - Volcanic Eruptions
What Is Inside a Volcano?
Popocatepetl, Mexico (17,802ft.)
magma chamber: the body of molten rock that feeds a volcano
vent: an opening at the surface of the Earth through which volcanic material passes

4. Ch.6, Sec.1 - Volcanic Eruptions
What Makes Up Magma?
- the key to whether an eruption will be explosive lies in the silica, water, and gas content of the magma
- if the water content is high, an explosive eruption is likely to occur due to high pressure in the rock, once it rises to the surface and turns gaseous (think about shaking a can of soda)
- if the silica content is high, an explosive eruption is likely to occur due to high pressure in the vents caused by built-up, hardened magma

5. Ch.6, Sec.1 - Volcanic Eruptions
What Erupts from a Volcano?
- explosive eruptions produce pyroclastic material (ash, blocks of rock, bombs of rock)
- nonexplosive eruptions produce liquid magma called lava (Pillow, Blocky, Aa, Pahoehoe)
Lava
1. Pillow Lava – forms when lava erupts underwater (low viscosity, so flows quickly)

6. Ch.6, Sec.1 - Volcanic Eruptions
2. Aa Lava – pours out quickly & forms a brittle crust (low viscosity, so flows quickly)
3. Blocky Lava – usually oozes out slowly & forms sharp-edged chunks (high viscosity, so flows slowly)
4. Pahoehoe Lava – flows very slowly with a glassy surface (high viscosity, so flows slowly)

7. Ch.6, Sec.1 - Volcanic Eruptions
Pyroclastic Material
1. Ash – forms when the gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny particles
2. Lapilli – forms from magma that has hardened before hitting the ground (also called cinders)

8. Ch.6, Sec.1 - Volcanic Eruptions
3. Volcanic Bomb – large blobs of magma that harden & spin in the air before landing
4. Volcanic Block – the largest pieces of pyroclastic material are made from solid rock

9. Ch.6, Sec.1 - Volcanic Eruptions
Pyroclastic Flows
- produced when enormous amounts of ash, dust, and gases are ejected from a volcano
- these flow at speeds of up to 125mph with temperatures reaching 1300°F!
- these flows can
create lahars, which are massive water-saturated mudflows, which have the consistency of wet cement