Primary Effects of Volcanoes

Overview

This lecture covers the primary effects of volcanic eruptions, focusing on the direct hazards they pose to people, property, and the environment.

Primary effects are immediate hazards from eruptions, including lava flows, pyroclastic flows, volcanic bombs, ash, and poisonous gases.
Ash can impact communities hundreds of miles away, making primary effects widespread and significant.

Lava flows are streams of molten rock that can travel tens of kilometers, particularly basaltic lava.
Lava flows can destroy property, ignite fires, and cause economic loss but typically move slowly enough for people to evacuate.
Fast-moving lava can reach up to 19 mph down steep slopes but is usually slower and predictable in path.
Lava can melt snow or ice, causing floods and mudflows, and sometimes explodes when contacting water or fuel.
Farmland and infrastructure buried by lava may be unusable for decades.

Pyroclastic flows are fast-moving, hot avalanches of gas, ash, and rock, moving over 60 mph and exceeding 100 km/h.
They are extremely deadly due to their speed, high temperature, and ability to overcome terrain.
Pyroclastic flows can result from erupting columns or the collapse of lava domes.
Surges are smaller, ash-laden flows separated from the main body, also highly destructive.
The 1902 Mount Pelée eruption destroyed Saint-Pierre, killing nearly 30,000 people with a pyroclastic flow.

Volcanic bombs are large blobs of molten rock ejected from a volcano, bigger than 2.5 inches in diameter.
They can travel kilometers from the vent, causing injury, death, or fires upon impact.
Damage is mainly due to direct impact or subsequent fires, with rare explosions as bombs cool.

Volcanic ash consists of fine particles that can be spread by wind over large distances.
Ash threatens air travel by damaging aircraft engines (e.g., 2010 Iceland eruption), disrupts transportation, and causes health risks when inhaled.
Ash can bury landscapes, kill crops, and collapse roofs under its weight, especially when wet.
Inhaling ash irritates skin, eyes, and lungs, especially dangerous to vulnerable populations.
Ash can reflect sunlight, causing temporary global cooling.

Volcanic gases are emitted during eruptions or from non-erupting volcanoes, including water vapor, carbon dioxide, and sulfur dioxide.
Some gases are toxic; CO₂ can build up in low areas and cause suffocation, as at Lake Nyos (1986).
Sulfur gases can irritate or poison at high concentrations and form acid rain.
Volcanic gas emissions can harm agriculture, property, and even alter climate.

Lava Flow — Stream of molten rock from a volcano that can destroy anything in its path.
Pyroclastic Flow — Rapid, hot avalanche of ash, gases, and rock fragments from a volcano.
Volcanic Bomb — Large, hot chunk of lava ejected from a volcano during explosions.
Volcanic Ash — Fine particles of rock and glass blasted into the air during eruptions.
Volcanic Gases — Gases released by volcanoes, including water vapor, CO₂, and sulfur dioxide.