Question

Explain why volcanic activity occurs in places other than plate boundaries.

Short answer

Volcanic activity away from plate boundaries occurs due to hotspots, where mantle plumes rise and create volcanoes.

Step-by-step solution

Understanding Volcanism

To explain volcanic activity away from plate boundaries, we must first understand that volcanism is a process where magma from the Earth's mantle rises to the surface, often due to weaknesses in the Earth's crust.

Identify Hotspots

Volcanic activity away from plate boundaries is often due to hotspots. A hotspot is a location where a mantle plume, an upwelling of abnormally hot rock, rises towards the Earth's surface, creating magma and eventually leading to volcanic eruptions.

Determine Plate Movement and Hotspots

Even though hotspots remain stationary, the tectonic plates above them can move. This movement causes the creation of a chain of volcanic islands as new parts of the crust pass over the hotspot, like the Hawaiian Islands.

Example of Intraplate Volcanism

The Hawaiian Islands are a prime example of hotspot volcanism. They are located in the middle of the Pacific Plate, away from any plate boundary, yet they have volcanic activity due to the underlying hotspot.

Key concepts

Hotspots

Hotspots are intriguing geothermal features of Earth that are responsible for volcanic activity away from tectonic plate boundaries. These are areas where unusually hot rock from deep within the Earth's mantle rises towards the surface. The presence of this hot rock creates conditions where magma can break through the Earth's crust, forming volcanoes. Generally, hotspots are stationary, but the tectonic plates above them move over time. This movement can lead to a series of volcanic islands being formed as the plate drifts over the hotspot. These islands may erupt independently and remain active for millions of years. The concept of hotspots explains why volcanic islands can exist far from any tectonic plate boundaries.

Mantle Plumes

Mantle plumes are the deep, underlying sources that feed hotspots. These are columns of upwelling hot rock from the Earth's mantle. The intense heat of a mantle plume causes melting of the mantle rock, producing magma. As the magma is less dense than the surrounding rocks, it begins to rise, sometimes making its way to the Earth's surface. Once there, it can form a volcano. These plumes are believed to originate near the boundary between the Earth's core and mantle, which is why they can be so persistent and stable over geological time. Their influence can be detected not just by surface volcanic activity, but also by geophysical methods such as seismic imaging.

Intraplate Volcanism

Intraplate volcanism is volcanic activity that happens within a tectonic plate rather than at its edges. It occurs primarily due to the presence of hotspots. Unlike at the margins of tectonic plates, where most volcanoes occur due to plate interactions, intraplate volcanism is fuelled by mantle plumes. These cause hotspots that create cracks in the crust, allowing magma to reach the Earth's surface. This type of volcanism is less common than that at plate boundaries, but it is responsible for some of the world's most famous volcanic islands and features. Examples include the Hawaiian Islands and Yellowstone in the United States.

Tectonic Plates

Tectonic plates are the large, rigid pieces of the Earth's lithosphere that fit together like a puzzle covering the planet. They are constantly moving, albeit very slowly, atop the flexible, semi-fluid asthenosphere beneath them. Most volcanic activity occurs at the boundaries of these plates, where they may converge, diverge, or slide past one another, causing magma to rise to the surface. However, hotspots can lead to volcanic activity right in the middle of these plates. As plates drift over stationary hotspots, chains of volcanoes and islands can form. This fascinating interplay between plate tectonics and hotspots provides insight into the dynamic nature of Earth's surface.

Hawaiian Islands

The Hawaiian Islands are a classic example of hotspot volcanism. Situated in the central Pacific Ocean, far from any tectonic plate boundaries, these islands are formed by a hotspot beneath the moving Pacific Plate. As the plate moves northwest over the hotspot, a series of volcanic islands and seamounts have formed over millions of years. Each island represents a different stage in volcanic life, with newer islands, like Hawaii, still showing active eruptions, while older islands in the chain become extinct as they drift away from the hotspot. The island of Hawaii is currently located directly above the hotspot, resulting in the active volcanoes of Mauna Loa and Kilauea. This phenomenon illustrates how stationary hotspots and moving tectonic plates can create dramatic and enduring geological features.