Chapter 6: Volcanoes

These flashcards cover key concepts related to volcanoes, including types of eruptions, volcanic structures, and magma properties.

What are the names of the two volcanoes compared in this chapter?

Mt. St. Helens and Kilauea.

What significant event occurred on May 18, 1980?

The eruption of Mt. St. Helens in Washington.

What type of magma is usually associated with less explosive eruptions?

Basaltic magma.

What is the result of high silica and gas content in magma?

It usually leads to explosive eruptions.

What is the typical temperature range of basaltic lava?

High temperature, low silica and gas content.

What type of volcanic eruption creates pyroclastic material?

Explosive eruptions.

What types of gases are commonly found dissolved in magma?

Mostly water and carbon dioxide.

What happens to magma pressure as gas content decreases?

The amount of gas decreases as pressure decreases.

What are pillow lavas?

Lava formations that occur as the outside surface cools quickly while the inside remains hot.

What is a caldera?

A very large circular depression at the top of a volcano, usually formed by the collapse of a magma chamber.

What are lahars?

Mudflows that result from the integration of volcanic debris and water.

What does decompression melting refer to?

Melting that occurs when the confining pressure decreases, thus lowering the melting temperature.

What happens at divergent boundaries concerning volcanic activity?

They produce the greatest volume of lava.

What are volcanic necks?

Resistant vents left standing after erosion has removed the volcanic cone.

What is the relationship between temperature and viscosity in magma?

As temperature increases, viscosity decreases.

What is a composite volcano (or stratovolcano)?

A tall, conical volcano built from alternating layers of lava, ash, and pyroclastic material, typically associated with explosive eruptions.

What are the characteristics of rhyolitic magma?

High silica content, high gas content, high viscosity, typically associated with explosive eruptions.

What type of volcanic activity is common at convergent plate boundaries where subduction occurs?

Explosive volcanism, forming volcanic arcs.

What are pahoehoe and A'a?

Two distinct types of basaltic lava flows based on their surface texture. Pahoehoe has a smooth, ropy surface, while A'a has a rough, blocky surface.

What is a cinder cone volcano?

A relatively small, steep-sided volcano built primarily from ejected lava fragments (cinders) that accumulate around a vent.

What is a pyroclastic flow?

A dense, fast-moving current of hot gas and volcanic debris (ash, pumice, and rock fragments) that flows down the side of a volcano, highly destructive and lethal.

What causes hot spot volcanism?

Volcanism that occurs away from plate boundaries, caused by a plume of hot mantle material rising from deep within the Earth to the surface.

What are the characteristics of andesitic magma?

Intermediate silica content, moderate gas content, moderate viscosity, typically associated with moderately explosive eruptions and often found at convergent plate boundaries.

What are volcanic bombs and blocks?

Volcanic bombs are semi-molten rock fragments that are ejected during an eruption and solidify in flight, acquiring aerodynamic shapes. Volcanic blocks are angular pieces of solid rock ejected during an eruption.

What is a shield volcano?

A broad, gently sloping volcano built by the eruption of fluid, basaltic lava flows, typically associated with non-explosive eruptions.

What characterizes lava domes?

Mound-shaped structures formed by the slow extrusion of highly viscous lava (often rhyolitic or andesitic) from a volcanic vent, typically associated with explosive eruptions.

What is a fissure eruption?

A volcanic eruption that occurs along an elongated crack or fracture in the Earth's crust, rather than from a central vent, often producing large volumes of fluid basaltic lava.

What is volcanic ash?

Finely pulverized rock, mineral, and volcanic glass fragments expelled from a volcano during an explosive eruption, typically less than 2 mm in diameter.

What is a volcanic crater?

A bowl-shaped depression at the summit of most volcanoes, typically less than 1 km in diameter, formed by the explosive eruption of material from the vent.

How are hot springs and geysers related to volcanic activity?

They are geothermal features where groundwater is heated by shallow magma bodies or hot igneous rocks, rising to the surface as hot water (hot springs) or intermittently erupting steam and water (geysers).

What are sills and dikes?

Sills are tabular igneous intrusions that run parallel to the layering of the surrounding rock, while dikes are tabular igneous intrusions that cut across the layering of the surrounding rock.

What is the primary difference between extrusive and intrusive igneous rocks?

Extrusive igneous rocks form when lava solidifies on the Earth's surface, cooling quickly and often having fine-grained textures. Intrusive igneous rocks form when magma solidifies beneath the Earth's surface, cooling slowly and typically having coarse-grained textures.

What is geothermal energy?

Energy derived from the Earth's internal heat, often harnessed in regions with volcanic activity or shallow hot rock, to generate electricity or directly heat buildings.

What are some additional volcanic hazards besides lahars and pyroclastic flows?

Ashfall (heavy deposition of volcanic ash), lava flows (though typically slow-moving, they destroy everything in their path), and volcanic gases (toxic gases like carbon dioxide and sulfur dioxide).

What is the difference between magma and lava?

Magma is molten rock found beneath the Earth's surface, while lava is molten rock that has erupted onto the Earth's surface.

What is viscosity in the context of magma?

Viscosity is a measure of a fluid's resistance to flow. In magma, it is primarily controlled by silica content and temperature, influencing eruption style.

What is tuff?

Tuff is a type of pyroclastic rock formed from volcanic ash and fragments ejected during an explosive eruption, which then consolidate.

What is a volcanic arc, and where are they typically found?

A volcanic arc is a chain of volcanoes formed above a subducting oceanic plate at a convergent plate boundary. Examples include the Andes Mountains and the Cascade Range.

What is the Pacific Ring of Fire?

The Pacific Ring of Fire is a major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur, caused by the movement and collisions of tectonic plates.