07 Volcanoes and Volcanism Free Online FlashCards

What is volcanism?

Volcanism is the movement of magma and volcanic gases from within Earth to or near its surface.

When is molten rock called lava rather than magma?

Magma is molten rock below ground; once it reaches the surface, it is called lava.

What causes decompression melting?

Decompression melting occurs when hot mantle rises and pressure decreases, allowing rock to melt without added heat.

What is viscosity, and how does silica content relate to it?

Viscosity is a fluid’s resistance to flow. Higher-silica magma is generally more viscous, while hot, low-silica basaltic magma is usually more fluid.

What characterizes an effusive eruption?

Effusive eruptions mainly pour out lava or produce lava fountains. Fluid basaltic lava may spread widely and build up layers.

What is volcanic ash made of, and how small are its particles?

Volcanic ash consists of volcanic material particles smaller than 2 millimeters; it is made of rock and volcanic glass, not combustion residue.

How does a shield volcano typically form?

A shield volcano is broad and gently sloping, built mainly by repeated flows of fluid lava.

What is a lahar, and what can produce one?

A lahar is a volcanic mudflow or debris flow that travels down valleys, forming when water mixes with loose volcanic material.

How does flux melting occur above a subduction zone?

In flux melting, water and other volatiles from a descending tectonic plate lower the melting temperature of nearby mantle.

How can rising magma cause heat-transfer melting?

Heat-transfer melting occurs when rising hot magma transfers heat to cooler surrounding crust, causing some of that rock to melt.

How can an explosive eruption produce a pyroclastic flow?

Explosive eruptions blast gas, ash, and larger rock fragments into the air. A collapsing eruption column can generate fast-moving pyroclastic flows.

What builds a cinder cone?

A cinder cone is usually a small, steep-sided cone formed as fragments ejected from a vent accumulate nearby; it commonly has a summit crater.