CE11 - Lecture 11 - Geohazards (Volcano)

Volcano

A vent, hill, or mountain that ejects molten rock, gases, and volcanic materials.

Magmatic eruption

Eruption caused by gas decompression within magma, propelling it forward.

Phreatic eruption

Steam-driven eruption without magma release, caused by superheated groundwater.

Phreatomagmatic eruption

Explosive eruption from water-magma interaction, releasing both vapor and magma.

Pahoehoe lava

Smooth, ropey lava with low viscosity and thin flow height.

Aa lava

Blocky, rough lava with high viscosity, forming thicker flows.

Pyroclastic materials

Rock fragments ejected by volcanic eruptions, classified by size (ash, lapilli, bombs).

Tephra fall

Volcanic fragments settling from the atmosphere, causing infrastructure damage and health hazards.

Pyroclastic density current (PDC)

Deadly fast-moving mix of hot gas, ash, and rock; includes pyroclastic flows and surges.

Lateral blast

Horizontal explosion of gas and ash, flattening everything in its path.

Volcanic gas

Gases like CO₂, SO₂, and HCl released during eruptions, posing toxic and climatic risks.

Lahar

Volcanic mudflow of water and sediments, triggered by rain or river mixing with deposits.

Debris avalanche

Catastrophic collapse of volcanic flanks, often triggering tsunamis.

Volcanic tsunami

Tsunami caused by volcanic material displacing water or underwater eruptions.

Ground deformation

Swelling or subsidence of the ground due to magma movement, causing fissures.

Active volcano

Erupted within the last 600 years or 10,000 years (based on deposits).

Potentially active volcano

Young-looking but no recorded eruptions.

PHIVOLCS Alert Levels

0 (Normal) to 5 (Hazardous eruption), guiding evacuation and danger zones.

Mayon Volcano PDZ

Permanent Danger Zone (6-8 km radius) where entry is restricted during unrest.

HazardHunterPH

DOST’s platform for accessing geohazard maps and disaster risk information.