Volcanoes Chapter 3 Section 2 Volcanic Activity

Characteristics of Magma Lava begins as magma in the mantle How does magma rise? Magma is less dense than the surrounding solid material. Magma flows upward into any cracks in the rock above. Magma rises until it reaches the surface.

Characteristics of Magma What does the force of a volcanic eruption depend upon? The amount of gas dissolved in the magma The thickness or thinness of the magma – thicker magma flows more slowly The temperature of the magma - the hotter the magma the more fluid it is The silica (material formed from oxygen and silicon) content of magma – the more silica the thicker the magma

Characteristics of Magma What is formed by magma? Magma that is high in silica forms: Rhyolite, which has the same composition as granite Obsidian forms when lava cools quickly Pumice forms when gas bubbles are trapped in cooling lava Magma that is low in silica forms: basalt

Stages of a Volcano Active – a volcano that is erupting or has shown signs that it may erupt in the near future.

Stages of a Volcano Largest active volcano - Mauna Loa in Hawaii rises 13,677 feet above sea level, it last erupted in 1984.

Stages of a Volcano Dormant – a volcano that will awaken sometime in the future and erupt (may be thousands of years later). Mount Rainier at 4,393 meters (14,410 feet) is the highest peak in the Cascade Range.

Stages of a Volcano Extinct – a volcano that is unlikely to erupt again. Crater Lake was formed after the collapse of an ancient volcano, posthumously named Mount Mazama. This volcano violently erupted approximately 7700 years ago. The basin was formed after the top 5000 feet of the volcano collapsed. Subsequent lava flows sealed the bottom, allowing the caldera to fill with approximately 4.6 trillion gallons of water from rainfall and snow melt, to create the seventh deepest lake in the world at 1,932 feet.

Other Types of Volcanic Activity Hot spring – forms when groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool. Little Hot Creek – temperatures in this pool can reach 80 C and it is lined with minerals and algae.

Other Types of Volcanic Activity Geyser – forms when rising hot water and steam becomes trapped underground in a narrow crack. As pressure builds the water and steam will erupt from the ground. Castle Geyser in Yellowstone National Park erupts water and steam.

Volcano Hazards Quiet Eruptions – lava flows pour from vents, setting fire to and then burying everything in their paths. Explosive Eruptions – hot burning clouds of gas burst out as well as cinders and bombs. Volcanic Ash – can bury entire towns. Landslides, and avalanches can occur as a result of a volcanic eruption.

Volcano Hazards Snow- and ice-capped volcanoes like Mount St. Helens are especially dangerous if they erupt. Much of the water in Mount St. Helens' mudflows came from snow and ice melted by the heat of the eruption. These mudflows were as thick as wet cement and able to carry along almost anything that they picked up.

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