Lava

001 Volcano eruption of Litli-Hrútur in Iceland in 2023 Photo by Giles Laurent

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Lava entering sea - Hawaii

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Lava is a molten rock that erupts onto the Earth's surface from a volcano or through a fissure, the latter being known as a volcanic vent. It is a primary feature of volcanic activity and plays a crucial role in the shaping of Earth's lithosphere. Upon cooling and solidification, lava forms igneous rock, which can be either basaltic, andesitic, dacitic, or rhyolitic, depending on its chemical composition and the rate of cooling.

Formation

Lava is formed when magma—molten rock located beneath the Earth's surface—rises due to buoyancy or external pressure, causing it to erupt through volcanoes or fissures. The temperature of erupting lava typically ranges from 700°C to 1,200°C (1,292°F to 2,192°F) depending on its composition. Basaltic lava, which has a low silica content, is hotter and more fluid than rhyolitic lava, which has a high silica content and is more viscous.

Types of Lava

Based on its viscosity and temperature, lava can be classified into several types:

• Pāhoehoe - A Hawaiian term for basaltic lava with a smooth, unbroken surface. It is relatively fluid and can form rope-like, smooth textures.
• ʻAʻā - Also originating from Hawaiian terminology, ʻAʻā describes basaltic lava that is more viscous than pāhoehoe, characterized by a rough, clinkery surface.
• Pillow lava - Forms when lava erupts underwater, leading to rounded structures that resemble pillows. This type is common at mid-ocean ridges and in ancient underwater volcanic sequences.
• Block lava - Has a higher viscosity than ʻAʻā and forms from andesitic or dacitic lava, characterized by a surface of smooth, large blocks.
• Lava domes - Result from the slow extrusion of viscous lava from a volcano, forming a dome-shaped feature.

Hazards

Lava flows pose significant hazards to life, property, and infrastructure. Their destructive force can obliterate everything in their path, although the speed of flow varies greatly depending on the type of lava and the slope of the terrain. Basaltic lava flows, being more fluid, can cover vast areas and travel at higher speeds. In contrast, more viscous lava flows, such as those from rhyolitic or dacitic eruptions, move slowly and tend to cover smaller areas but can still cause significant damage.

Cultural and Scientific Importance

Lava has played a significant role in shaping the Earth's surface and is of great interest to geologists who study its composition, flow patterns, and the structures it forms to understand the Earth's volcanic activity and history. Culturally, lava is significant in many regions with active or historic volcanic activity, where it is often intertwined with local mythology and regarded with respect and awe.