Volcanism types based on the flow of lava are primarily characterized by the viscosity and composition of the lava, which influence how it flows and the landforms it creates. The two main types of volcanic eruptions based on lava flow are effusive eruptions and explosive eruptions.
1. Effusive Eruptions
Effusive eruptions involve the relatively gentle outpouring of lava onto the Earth’s surface. These eruptions typically occur at hotspots or divergent plate boundaries where magma is relatively low in viscosity and gas content.
a. Types of Lava Flows
- Basaltic Lava Flows:
- Description: Basaltic lava flows are characterized by low viscosity and high temperatures, allowing the lava to flow rapidly and cover large areas.
- Example: Hawaiian Islands, where shield volcanoes like Mauna Loa and Kilauea produce extensive basaltic lava flows. The ongoing eruption of Kilauea since 1983 has produced numerous lava flows that have expanded the island’s coastline.
- Pahoehoe Lava Flows:
- Description: Pahoehoe lava flows are smooth, rope-like lava flows with a shiny surface formed by the rapid cooling and solidification of the lava.
- Example: The 1984 eruption of Mauna Loa in Hawaii produced pahoehoe lava flows that traveled over 15 kilometers from the vent.
- Aa Lava Flows:
- Description: Aa lava flows are rough, jagged lava flows with a blocky surface formed by the slow movement and cooling of the lava.
- Example: The eruption of Eldfell volcano on the island of Heimaey, Iceland, in 1973 produced aa lava flows that threatened the town but were successfully diverted.
b. Lava Tubes
- Lava Tubes:
- Description: Lava tubes are underground tunnels formed by the flow of lava beneath a solidified crust. They can transport lava over long distances and protect it from cooling.
- Example: The Thurston Lava Tube in Hawaii Volcanoes National Park on the island of Hawaii is a popular tourist attraction formed by the Kilauea eruption.
c. Volcanic Features
- Shield Volcanoes:
- Description: Shield volcanoes are broad, gently sloping volcanic landforms built up by the accumulation of successive lava flows.
- Example: Mauna Loa and Kilauea in Hawaii are classic examples of shield volcanoes formed by effusive eruptions.
- Lava Plateaus:
- Description: Lava plateaus are extensive, flat areas covered with layers of basaltic lava flows, often resulting from effusive eruptions.
- Example: The Columbia River Basalt Group in the Pacific Northwest of the United States is one of the largest lava plateau provinces in the world.
2. Explosive Eruptions
Explosive eruptions involve the sudden release of gas and pressure from highly viscous magma, resulting in violent explosions that eject volcanic ash, rocks, and gases into the atmosphere.
a. Types of Explosive Eruptions
- Andesitic to Rhyolitic Explosive Eruptions:
- Description: These eruptions involve highly viscous magma with high gas content, leading to explosive fragmentation and eruption columns.
- Example: The 1991 eruption of Mount Pinatubo in the Philippines was a rhyolitic explosive eruption that ejected large volumes of ash and gases into the atmosphere, leading to global cooling.
- Plinian Eruptions:
- Description: Plinian eruptions are highly explosive eruptions characterized by tall eruption columns reaching several kilometers into the atmosphere.
- Example: The eruption of Mount Vesuvius in AD 79 was a Plinian eruption that buried the cities of Pompeii and Herculaneum under volcanic ash and pyroclastic flows.
b. Volcanic Features
- Stratovolcanoes (Composite Volcanoes):
- Description: Stratovolcanoes are steep-sided, symmetrical volcanic landforms built up by alternating layers of lava flows, volcanic ash, and other volcanic debris.
- Example: Mount Fuji in Japan and Mount St. Helens in the USA are examples of stratovolcanoes formed by explosive eruptions.
- Calderas:
- Description: Calderas are large, basin-shaped depressions formed by the collapse of the summit area following a massive explosive eruption or magma withdrawal.
- Example: The Yellowstone Caldera in Wyoming, USA, is one of the largest calderas in the world, formed by several supereruptions over millions of years.
Conclusion
Volcanism types based on the flow of lava encompass a wide range of eruptive styles and associated landforms. Effusive eruptions, characterized by the gentle outpouring of lava, create features such as shield volcanoes, lava plateaus, and lava tubes. Explosive eruptions, involving the sudden release of gas and pressure, lead to the formation of stratovolcanoes, calderas, and Plinian eruption columns. Understanding these volcanic processes and landforms is essential for assessing volcanic hazards and mitigating risks in volcanic regions.
