ES1002 Week 3: Volcanics and Geothermal Resources

What is a volcano?

A vent through which volcanic material (lava, pyroclasts, gas) escapes.

What is the typical source of volcanic melt?

The mantle.

What are the two main types of melting that generate magma?

Decompression melting and volatile-assisted melting.

What factors control the viscosity of magma/lava?

Composition, crystal content, gas content, and temperature.

How can viscosity be increased?

Higher SiO₂, more bubbles, more crystals.

How can viscosity be decreased?

Higher temperatures and more dissolved gas.

What is melt rheology?

A control on the eruption style and landforms of a volcanic eruption.

What happens to viscosity as silicate content increases?

Viscosity increases.

What are the three main factors controlling eruption style?

Rheology, dissolved volatile content, and magma ascent rate.

What gases are most abundant in magma?

Water (H₂O), CO₂, and SO₂.

What are vesicles?

Gas bubbles trapped in volcanic rocks.

What is pumice?

Volcanic rock with a frothy texture formed from explosive eruptions.

Why are volcanic eruptions explosive?

Dissolved volatiles expand rapidly when reaching atmospheric pressure.

What are pyroclasts?

Fragments of magma or rock ejected during explosive eruptions.

How does water increase explosivity?

Water turns to steam and expands rapidly, increasing pressure.

What is dome collapse?

A lava dome oversteps the crater edge, breaks apart, and reduces pressure, leading to explosions.

What is the Icelandic eruption style?

Gentle eruptions of basalt magma.

What is Strombolian eruption style?

Gas bubbles coalesce and pop, creating small explosions.

What is a Vulcanian eruption?

Short, violent cannon-like explosions with high exit velocities.

What is a Plinian eruption?

Very explosive, with sustained eruption columns up to 25 km high.

What is a Pelean eruption?

Deadly, dome-collapse driven pyroclastic flows with temperatures of 400–700°C.

What is a phreatic eruption?

Eruption caused by water reacting with magma, producing ash.

What is a phreatomagmatic eruption?

Water and magma reaction that is highly explosive.

What can volcanic deposits tell us?

Eruption style, size, dynamics, and impacts.

What are lava tubes?

Channels within lava flows enclosed by solid crust.

What are features of mafic lava flows?

Ropy textures, steep sides, and central faster flow.

What are columnar joints?

Cracks in cooling basalt lava, forming hexagonal columns.

What does pillow lava indicate?

Underwater eruption with dissolved gases.

What is tephra?

A general term for all pyroclastic material.

How are pyroclastic rocks classified?

By particle size and origin (juvenile or non-juvenile).

What are pyroclastic fall deposits?

Parallel-bedded, well-sorted layers from fallout of an eruption column.

What are pyroclastic flow deposits?

Poorly sorted avalanches of hot ash and gas that follow topography.

What are pyroclastic surge deposits?

Fine-grained, cross-bedded, gas-dominated flows that can climb terrain.

What is the Volcanic Explosivity Index (VEI)?

A scale from 0 (quiet) to 8 (super-eruption) indicating eruption size.

How frequent are VEI 8 eruptions?

About once every 100,000 years.

What are primary volcanic hazards?

Lava flows, pyroclastic flows, ash clouds, and gas emissions.

What are the characteristics of lava flow hazards?

Cause property damage, travel 1–50 km/h, not very lethal.

What are the characteristics of pyroclastic flows?

Move 100–300 km/h, up to 1000°C, cause death by suffocation or burning.

What are the hazards of ash clouds?

Collapse buildings, poison soil, harm health, and disrupt aviation.

What are secondary volcanic hazards?

Lahars (mudflows), tsunamis, and long-term climate effects.

What are lahars?

Fast, dense flows of volcanic debris mixed with water.

How can volcanoes impact the global climate?

Ash and gases enter the stratosphere, cooling the planet.

What are some societal impacts of eruptions?

Death, crop failure, food shortages, and mass migration.

What are benefits of living near volcanoes?

Fertile soil, mineral deposits, tourism, and geothermal energy.

What is geothermal energy?

Energy from Earth's heat, especially accessible in volcanic areas.

What is the formula for extracting heat from rock?

Heat = density × heat capacity × volume × Δ temperature.

What are some environmental risks of geothermal energy?

High costs, impact on water tables, and potential volcanic hazards.

How are volcanoes monitored?

Seismometers, ground deformation (GPS/tilt), and gas emission analysi