Unit 8 (Ryan) MS Volcanoes

1. What is a composite volcano?

A composite volcano forms the tall cone shape you usually think of when you think of a volcano. Composite volcanoes have broad bases and steep sides. These volcanoes usually have a large crater at the top.

1. What is a hot spot?

A hot spot is a place where volcanoes can be found. Some volcanoes form over active hot spots. Scientists count about 50 hotspots on the Earth. Hot spots may be in the middle of a tectonic plate.

1. Describe what happens during an explosive volcanic eruption.

An explosive eruption produces huge clouds of volcanic ash. Chunks of the volcano fly high into the atmosphere. Explosive eruptions can be 10,000 times as powerful as an atomic bomb. Hot magma beneath the surface mixes with water. This forms gases. The gas pressure grows until it must be released. The volcano erupts in an enormous explosion.

3. Why do hotspot volcanoes form in lines?

As the tectonic plates move above a hot spot, they form a chain of volcanoes. A volcano will eventually rise above sea level and join the other volcanoes or create a new island.

4. What plate tectonic setting produces the most volcanoes?

At divergent plate boundaries (ocean ridges or rifts) and at convergent plate boundaries at subduction zones.

6. How does a cinder cone form?

Cinder cones are composed of small fragments of rock, called cinders. The cinders are piled on top of one another. These volcanoes usually do not produce streams of lava. Cinder cones often form near larger volcanoes (near composite and shield volcanoes). Cinder cones most of the time only produce one eruption. For this reason, they do not reach the sizes of the other larger volcanoes.

5. What is a cinder cone?

Cinder cones are small, cone-shaped volcanoes. Cinder cones are the smallest and most common type of volcano. Cinder cones have steep sides like composite volcanoes. They are much smaller, rarely reaching even 300 meters in height. Cinder cones usually have a crater at the summit.

3. What are pyroclasts?

Hot fragments of rock.

5. The boiling point of water is 100 degrees C. Why might water make an eruption more explosive?

Hot magma beneath the surface mixes with water. This forms gases. The gas pressure grows until it must be released. The volcano erupts in a large explosion.

2. How is a hotspot related to a mantle plume?

Hot spots lie directly above mantle plumes (column of hot rock). Mantle plumes continuously bring magma up from the mantle towards the crust.

3. What types of landforms are created by lava?

Hot springs and geysers are also formed by lava (and water as well). If there is enough lava it can also flow out into the water creating new land and building onto islands.

5. Are the oceans being taken over by land? Why or Why not?

I'd say yes, just very slowly. Volcanic eruptions build onto land as the lava flows out into the oceans. Water isn't taking over land, it's actually helping create new land by hardening lava quickly to create large chunks of igneous land. Every eruption (mainly the volcanoes by water, or on islands) adds to land little by little.

• Lava dome:

If thick lava makes it to the surface, it cannot flow for from the vent. It often stays right in the middle of a crater at the top of a volcano. Here the lava creates a large, round lava dome.

2. What types of landforms form from intrusive igneous activity?

Intrusions become land formations if they are exposed at the surface by erosion. The granite intrusions that form the Sierra Nevada in California are well exposed and have been formed by intrusive igneous activity.

• Lava Plateau:

Made of a large amount of lava. The lava flows over a large area and cools. This creates a large, flat surface of igneous rock. Lava plateaus may be huge.

4. What is a magma chamber and what are its characteristics?

Magma collects in magma chambers beneath Earth's surface. Hence the name "magma chamber". Magma chambers are located where the heat and pressure are great enough to melt rock. These locations are at divergent or convergent plate boundaries or at hotspots.

• Intrusion:

Magma that cools underground forms intrusions. Intrusions become land formations if they are exposed at the surface by erosion.

4. How does new land form?

New land forms when volcanoes erupt and lava flows out into the water. It quickly hardens and builds onto land, adding onto islands and creating new land.

2. Describe what happens during a non-explosive volcanic eruption?

Non-explosive eruptions happen when there is little or no gas. The lava is thin, fluid and runny. It flows over the ground like a river.

6. Why is predicting volcanic eruptions so important?

Predicting volcanic eruptions are extremely important because these eruptions can be very devastating, particularly to the people who live close to volcanoes.

3. What is a shield volcano?

Shield volcanoes are huge, gently sloping volcanoes. A shield volcano has a very wide base. It is much flatter on top than a composite volcano. Shield volcanos are very large. For example, the Mauna Loa Volcano has a diameter of more than 70 miles.

7. What factors are considered in predicting volcanic eruptions?

Some signs that a volcano may soon erupt include an increase in earthquakes, surface bulging and released gases that can be monitored by scientists.

2. How does a composite volcano form?

The crater was created during the volcano's last eruption. The composite volcano itself is formed by alternating layers (strata) of magma and ash. The magma that creates composite volcanoes tends to be thick. The steep sides form because the lava can't flow too far from the vent. When it erupts much of the ash and pyroclast falls back down near the vent. This creates the steep sides of composite volcanos.

4. How does a shield volcano form?

The lava that creates shield volcanoes is relatively thin. The thin lava spreads out. This builds a large, flat volcano layer by layer. Shield volcanos often form along divergent plate boundaries. They also form at hot spots, like Hawaii. These eruptions are non-explosive.

• Geyser:

Water may become superheated by magma. It becomes trapped in a narrow passageway. The heat and pressure build as more water is added. When the pressure is too much, the superheated water bursts out onto the surface.

• Hot Spring:

When hot water gently rises to the surface, it creates a hot spring. A hot spring forms where a crack in the Earth allows water to reach the surface after being heated underground.