Volcanoes

I. Volcano = an opening in the Earth’s crust that allows magma to reach the Earth’s surface

A. Development; usually a cone of volcanic material forms with a bowl shaped vent at the top called a crater

1. Some craters are so big they are called calderas

a. Calderas are usually on long dormant volcanoes and eventually become lakes

b. Some calderas form when the underground magma chamber empties and the ground can no longer support the weight of the cone

B. During the eruption magma is forced through the crack and is exposed to the Earth’s surface; at this point it becomes Lava

1. Magma; molten rock within the Earth

a. This is lighter than solid rock so it rises to the surface

b. Intrusion sometimes occurs; this is when this molten rock hardens before it reaches the surface

c. Thin magma rises easily forming lava flows that may stream great distances

d. Thick magma may rise explosively to the surface

· lava is thrown into the air building the volcanic mountain

2. Lava is molten rock a the Earth’s surface

a. Sometimes lava that is thrown into the air will harden and form Lava Bombs

3. Cinders are hardened “pebbles” of lava that are thrown in the air

4. Ash is particles of Lava that are less than 2 mm in size

C. Types of Volcanoes

1. Composite – Made of alternating layers of ash, cinder and lava

a. average in size and steepness

b. Mt. Fuji and Mt. Vesuvius

2. Cinder Cone – mainly ashe and tuff, (tuff is compressed ash, cinder and lava bombs)

a. they are the steepest

b. common in Central America

c. Formed at areas of convergence

3. Shield – rounded gentle slopes and their bases cover a wide area

a. the lava is very fluid and flows easily

b. the form at areas of convergence and divergence

· Hawaiian Islands

4. Sea Mount – underwater volcano that resembles Cinder Cone

5. Guyot – inactive seamount only with a flattened top

D. Eruptions can be violent and can cause damage several ways; (often termed the “crisis”)

1. The lava is charged with steam and other gases

a. Carbon Dioxide, Hydrogen, Carbon Monoxide and Sulfur Dioxide usually in poisonous clouds

b. These clouds often rain bringing these poisons with them

c. Lightning can be generated within these volcanic clouds especially if it is high with dust particles