Volcano Types, Eruptions & Supervolcanoes

Types of Volcanoes

• SHIELD VOLCANOES: Large, broad slopes with fluid lava flow (e.g., Mauna Loa, Hawaii).
• COMPOSITE VOLCANOES: Steep and symmetrical, explosive (e.g., Mayon, Philippines).
• LAVA DOMES: Oozes viscous lava.
• CINDER CONES: Smallest, single vent, erupts cinders, ash, and rocks (e.g., Sunset Crater, Arizona; Showa Shinzan, Japan).

Volcanic Eruption and Hazards

• Melting ice causes glaciers to retreat, which reduces pressure on the ground below, making landslides more susceptible.
• Landslides expose magma chambers, bringing magma closer to the surface, increasing the chance of eruptions.
• The world has about 1,350 potentially active volcanoes, with about 500 having erupted in recorded history.
• Volcanic eruptions can be underwater which may affect atmospheric temperature with droplets of sulfuric acid and ash.
• "Volcanic Winter" is named from the obscured sun's light.

Supervolcanoes

• Supervolcanoes have infrequent but large-scale eruptions.
• Once or more eruptions can occur.
• The most famous active supervolcano is Yellowstone Caldera (USA).

Deadliest Volcanic Eruption

• The deadliest eruption was the 1815 Mount Tambora eruption in Indonesia.
• This eruption led to global climate changes, causing 1816 to be known as "The year without a summer".
• The eruption expelled 24 cubic miles of ash, pumice, and aerosols into the atmosphere, and 60 megatons of sulfur.
• Casualties were between 71,000 and 250,000.

Taal Volcano

• Taal Volcano Island is 23 square kilometers in area, the highest point is 311 meters above sea level (SW rim of the Main Crater).
• It has at least 35 eruption cones and 47 craters/depressions formed by explosive eruptions or collapsed subsidence.
• Taal's Main Crater is 1.9 km in diameter, and the Taal Caldera is 25 km across.
• The underwater bathymetry suggests about 35 different volcanic landforms, indicating numerous and complex eruption centers that may erupt from any other points.

Lahar

• A lahar is a destructive volcanic mudflow composed of water, volcanic ash, rock fragments, and debris that moves down the slopes of a volcano.
• Lahars can be triggered by heavy rainfall, melting snow/ice, or sudden release of water from crater lakes.
• They flow like wet concrete and can travel at speeds up to 60 km/h, occurring during or long after an eruption.
• Lahars bury and destroy communities, infrastructure, and farmlands, and can persist for years, repeatedly affecting areas near volcanoes.
• The 1991 Mount Pinatubo eruption in the Philippines caused lahar flows that devastated Central Luzon.

Ash Fall

• Volcanic ash fall happens when fine particles of fragmented rock, minerals, and volcanic glass eject into the atmosphere and settle back to the ground.
• Volcanic ash blankets the Philippines.
• Mount Kanlaon erupts and blasts hot ash into the sky.
• Volcanic ash can cause respiratory issues and skin/eye irritation, and leads to roof collapses due to accumulation.
• Volcanic ash can travel thousands of kilometers depending on wind direction and can range from a thin dusting to several meters thick.
• Volcanic ash is composed of very fine, abrasive particles that can damage lungs, machinery, and infrastructure.

Pyroclastic Flow

• A pyroclastic flow is a fast-moving current of hot gas, ash, and volcanic debris that travels down the slopes of a volcano.
• Pyroclastic flows can reach speeds of over 700 km/h and temperatures exceeding 1,000°C.
• They are caused by the collapse of an eruptive column or a lava dome.
• These flows cause instant destruction and fatalities due to extreme heat and speed, leaving behind thick layers of ash and rock.
• The 1902 eruption of Mount Pelée in Martinique killed nearly 30,000 people within minutes.

Ballistic Projectile

• Ballistic projectiles are large fragments of rock or lava ejected from a volcano during an eruption, following a curved path due to gravity.
• They can cause severe injuries, death, and structural damage upon impact, affecting areas close to the volcano (usually within 5 km).
• These projectiles can travel at speeds of 200 m/s and reach distances of several kilometers.
• They include bombs, blocks, and other fragments larger than 64 mm in diameter.
• Does not follow wind patterns, unlike ash falls.

Volcanic Glasses

• Volcanic glasses include obsidian, pumice, and volcanic ash.
• They are hard and brittle but lack a defined crystal structure.
• Volcanic glasses are often sharp and abrasive, causing respiratory problems when inhaled (e.g., silicosis).
• They are also used in industrial applications like abrasives, cutting tools, and insulation.
• Pumice rock is the only rock that floats on water.

Lava Flow

• A lava flow is molten rock that emerges from a volcano and moves across the ground before cooling and solidifying.
• Lava can move at varying speeds, from slow-moving (pāhoehoe lava) to fast and rough ('A'ā lava).
• Its temperature ranges from 700°C to 1,200°C and it can extend for kilometers but usually moves at a walking pace, allowing evacuation.
• Eruptions from the Iceland Volcano have been spewing lava 7 times in 2024.
• Kilauea Volcano in Hawaii had eruptions with lava gushing to the surface.
• Lava burns and buries everything in its path, creating new landforms and altering landscapes.
• Example: The 2018 Kilauea eruption in Hawaii destroyed hundreds of homes with lava flows.