types of volcanoes

eruptions at composite volcanoes

Viscous lava cannot travel far down the sides of the volcano before it solidifies, which creates the steep slopes of a composite volcano. In some eruptions the pressure builds up so much that the material explodes as ash and small rocks. The volcano is constructed layer by layer, as ash and lava solidify, one upon the other (Figure 1.3). The result is the classic cone shape of composite volcanoes. Mount St. Helens was a beautiful, classic, cone-shaped volcano. In May 1980 the volcano blew its top off in an explosive eruption, losing 1,300 feet off its summit. Mt. Fuji in Japan is one of the worlds most easily recognized composite volca- noes.

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shield volcanoes

Shield volcanoes get their name from their shape. Although shield volcanoes are not steep, they may be very large. Shield volcanoes are common at spreading centers or intraplate hot spots (Figure 1.4). Hawaii has some spectacular shield volcanoes including Mauna Kea, which is the largest mountain on Earth from base to top. The mountain stands 33,500 ft high, about 4,000 feet greater than the tallest mountain above sea level, Mt. Everest. A cross section of a composite volcano reveals alternating layers of rock and ash: (1) magma chamber, (2) bedrock, (3) pipe, (4) ash layers, (5) lava layers, (6) lava flow, (7) vent, (8) lava, (9) ash cloud. Frequently there is a large crater at the top from the last eruption. Mauna Kea on the Big Island of Hawaii is a classic shield volcano.

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eruptions at shield volcanoes

The lava that creates shield volcanoes is fluid and flows easily. The spreading lava creates the shield shape. Shield volcanoes are built by many layers over time and the layers are usually of very similar composition. The low viscosity also means that shield eruptions are non-explosive.

cinder cones

Cinder cones are the most common type of volcano. A cinder cone has a cone shape, but is much smaller than a composite volcano. Cinder cones rarely reach 300 meters in height, but they have steep sides. Cinder cones grow rapidly, usually from a single eruption cycle. These volcanoes usually flank shield or composite volcanoes. Many cinder cones are found in Hawaii. A lava fountain erupts from Puu Oo, a cinder cone on Kilauea.

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eruptions at cinder cones

Cinder cones are composed of small fragments of rock, such as pumice, piled on top of one another. The rock shoots up in the air and doesnt fall far from the vent. The exact composition of a cinder cone depends on the composition of the lava ejected from the volcano. Cinder cones usually have a crater at the summit. Most cinder cones are active only for a single eruption. Click image to the left or use the URL below. URL:

composite volcanoes

Composite volcanoes are constructed of felsic to intermediate rock. The viscosity of the lava means that eruptions at these volcanoes are often explosive.

volcanoes

A volcano is a vent through which molten rock and gas escape from a magma chamber. Volcanoes differ in many features, such as height, shape, and slope steepness. Some volcanoes are tall cones and others are just cracks in the ground (Figure 1.1). As you might expect, the shape of a volcano is related to the composition of its magma.

instructional diagrams

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questions

since it hasnt had a large eruption since 1980, mount st. helens is considered extinct.

a) true

-->  b) false

which of these are characteristics of composite volcanoes?

a) always have a pointy top, like a classic volcano.

b) are not associated with cinder cones.

-->  c) eruptions often explosive.

d) all of the above

this determines both eruption type and volcano type.

-->  a) magma composition

b) plate tectonic setting

c) temperature of eruption

d) pressure of eruption

shield volcanoes are common at intraplate hot spots.

-->  a) true

b) false

this is the largest shield volcano on earth.

a) mt. everest

-->  b) mauna kea

c) mt. shasta

d) mt. fuji

mt. fuji is this type of volcano.

a) cinder-cone

b) shield

-->  c) composite

d) dormant

shield volcanoes

a) are usually made of material from one eruption.

b) have lavas of many different compositions.

-->  c) are made of low viscosity lavas.

d) all of these.

cinder cones

-->  a) can be made of magma of any composition that can make a volcano

b) are usually made from several different eruptions of material.

c) are usually in cinder cone fields not associated with other volcanoes.

d) all of these.

cinder cones have a cone shape because

a) lava doesnt flow far from the vent.

b) lava flows downhill in a cone shape.

c) erosion by wind and rain shapes the volcano in a cone shape.

-->  d) rock fragments shoot up in the air and then fall back to the ground.

diagram questions

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