DRRR 11: Volcano Hazards

Volcano

It is an opening in the Earth's crust that allows molten rock (magma), gases, and debris to escape to the surface, where magma becomes lava.

Magma

It is molten rock that is found within the earth; will be formed after the water has reduced the melting point of the rocks underneath.

Lava

Molten rock released from the earths mantle.

Convergent Plate Boundary

This occurs when Earth’s plates move towards each other, causing subduction (oceanic sinking) or mountain building, forming volcanoes and deep trenches.

Divergent Plate Boundary

This occurs when Earth’s plates move away from each other, creating new crust through volcanic activity, resulting in rift valleys and mid-ocean ridges.

Along Earth’s plate boundaries and hotspots.

Where are volcanoes usually located?

Main Vent

The channel magma travels through to reach Earth’s surface.

Magma Chamber

A storage location of molten rock below the ground.

Crater

The top of the volcano where magma erupts from.

Composite Volcano

A type of volcano that has the following characteristics:

• Viscous (thick) lava that is acidic

• Erupt violently

• Steep sides

• Located on convergent plate boundaries

Examples include: Mount Mayon, Mount Kanlaon, Mount St. Helens, Mount Etna

Shield Volcano

A type of volcano that has the following characteristics:

• Runny, non-acidic lava

• Gentle sides

• Less violent eruptions

• Located on hotspots or on divergent plate boundaries

Examples include: Mauna Loa, Mauna Kea

Lahar

A volcano hazard that is of Indonesian origin for “lava” or “lava flow,” which volcanologists adapted to describe it as a wet, cement-like mixture of volcanic ash, debris and water flow.

Primary/Hot Lahar

Lahar that is directly associated with a volcanic eruption.

Secondary/Cold Lahar

Lahar that is caused by heavy rainfall.

Tephra Falls

These are generally fragmented volcanic particles. They are showers of fine to coarse-grained volcanic materials and other airborne products of a volcanic eruption.

• <2mm diameter - ash

• 2-64mm diameter - lapilli

• >64mm diameter - blocks and bombs

Pyroclastic Flow

This refers to hot, dry masses of fragmented volcanic materials that move along the slope and the ground surface at a speed greater than 60 km per hour. This flows from a collapsed eruption column or lava dome.

Pyroclastic Density Currents

These are the materials released from the mouth of the volcano, such as pyroclastic, hot gases, and ashes.

• Classifications:

  • Pyroclastic Flow—a dense type that moves a bit slower compared to a surge

  • Pyroclastic Surge—a diluted type that has more mobility

Ballistic Projectiles

These are rocks (blocks or bombs) that are released into the air by an erupting volcano. These land between 2 km of the vent but can travel as far as 5 km or further if the eruption is explosive.

Volcanic Gases

One of the volatile compounds released from magma.

Water Vapor

A volcanic gas that is colorless, odorless, harmless, and the most abundant of them all.

Carbon Dioxide (CO₂)

A volcanic gas that is colorless and odorless; it can accumulate in low areas and be deadly in high concentrations.

Sulfur Dioxide (SO₂)

A volcanic gas that has a pungent odor; irritates eyes, skin, and lungs.

Hydrogen Sulfide (H₂S)

A volcanic gas that has a strong rotten-egg smell; highly toxic even at low levels.

Hydrogen Halides (HF, HCl, HBr)

A volcanic gas that is toxic and can contribute to acid rain. It is poisonous to sources of drinking water and vegetation.

Lava Flow

It is a mass of magma that flows down slowly the slope of the volcano; some can move fast on steep slopes. These destroy anything in their path, but they usually do not move fast enough to outrun people.

• The silica content determines the travel speed of this hazard:

  • Low silica magma: low viscosity, high speed

  • High silica magma: high viscosity, low speed

• The frequency and intensity of earthquakes felt within the area increase. As pressure keeps building up. It releases more seismic energy that causes ground shaking in the area.

• The release of steam and gases from the vents near the volcano increases. From afar, it may be seen only as a cloud of air.

• The fumarolic activity increases. Fumaroles near the mouth of the volcano not only emit gases but also show a noticeable increase in carbon dioxide concentration in the air.

• Heat emission increases. The temperature within the area increases dramatically. It is an indicator that magma is close to the surface.

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• Ground elevation (tilting) and ground fissuring (cracks) are visible. Rocks are slowly being pushed upward from the mouth of the volcano, affecting areas adjacent to it.

• Flowing lava with red-orange colors is visible at the mouth of the volcano. The magma enclosed underneath has started to release pressure.

• There is a change in the color of vegetation, an indicator of an increased volume of volcanic gases emitted

• Landslides are brought about by volcanic activity.

• Springs or bodies of water within the area are drying up.

These are the signs of an impending volcanic eruption according to the USGS (2021) and Rimando (2016).

• Determine your risk: Know if you reside within a danger zone (typically a 14-kilometer radius from the crater).

• Prepare a "Go Bag": Pack essentials including drinking water, non-perishable food, clothes, and necessary masks.

• Learn Evacuation Plans: Familiarize yourself with the specific evacuation areas designated by your local authorities or barangay.

• Coordinate Transportation: Arrange a ride-sharing plan with relatives or neighbors if you do not have your own vehicle.

• Stay Informed: Understand the different volcanic alert levels and the specific history of the nearby volcano.

The things you need to do before an eruption.

1. Evacuate Immediately: If you are near the volcano, your priority is to flee the area, as volcanic emissions are extremely harmful.

2. Seal Your Home: Close all doors and windows and cover gaps with wet cloths to block ash fall.

3. Protect Food and Water: Ensure all consumables are properly covered to avoid ingestion of toxic ash.

4. Stay Indoors and Mask Up: If you cannot leave, stay inside and wear goggles and a mask (or a wet handkerchief) to protect your eyes and respiratory system.

The things you need to do during an eruption.

• Wait for Official Clearance: Do not return to your home until authorities provide a formal "go signal".

• Seek Medical Advice: Consult a doctor if you believe you have inhaled a significant amount of volcanic ash.

• Inspect Structures: If earthquakes occurred during the eruption, have your home checked for structural integrity before moving back in.

• Clean Ash Safely: When cleaning, sweep the dry ash into sacks rather than drenching it with water, which can clog canals and drainage systems.

The things you need to do after an eruption.

1. Reduced economic activity

2. Danger to life and damage to property and facilities

3. Damage to habitats and the landscape

These are the negative effects of volcanic eruptions.

1. Areas where magma lies can be used to produce geothermal energy

2. Volcanic ash can be used as a soil fertilizer

3. Increase in tourists who are interested in visiting the volcano

These are the positive effects of volcanic eruptions.