Decompression Melting

Definition

Decompression melting is the process by which magma forms when the pressure on hot, solid mantle rocks is reduced, allowing them to melt. This typically occurs at divergent plate boundaries or hotspot locations, where tectonic forces create a decrease in pressure, leading to the formation of magma that can rise to the Earth's surface. It plays a crucial role in understanding how magma is generated and contributes to volcanic activity.

5 Must Know Facts For Your Next Test

1. Decompression melting is most commonly observed at mid-ocean ridges, where tectonic plates are pulling apart and reducing pressure on the underlying mantle.
2. As the pressure decreases during decompression melting, the temperature of the mantle rock remains high enough to initiate melting without requiring an increase in temperature.
3. The process allows for the generation of basaltic magma, which is less viscous and flows more easily than other types of magma.
4. Decompression melting can also occur beneath volcanic hotspots, where rising plumes of hot mantle material reduce pressure as they ascend.
5. Understanding decompression melting helps explain volcanic eruptions associated with both mid-ocean ridges and hotspots, providing insights into volcanic processes and magma composition.

Review Questions

• How does decompression melting contribute to magma formation at divergent plate boundaries?
  • At divergent plate boundaries, tectonic plates move apart, causing a reduction in pressure on the underlying mantle rocks. This decrease in pressure allows these hot mantle rocks to melt without requiring an increase in temperature. The resulting magma can then rise to fill the gap created by the separating plates, leading to the formation of new oceanic crust and contributing to volcanic activity.
• Discuss the relationship between decompression melting and volcanic hotspots, including how this process differs from other forms of magma generation.
  • In volcanic hotspots, decompression melting occurs as hot mantle plumes rise toward the Earth's surface. As these plumes encounter lower pressure at shallower depths, the mantle material begins to melt, generating magma. This process is distinct from other forms of magma generation that may involve increasing temperatures or flux melting due to added water or carbon dioxide. Hotspot volcanism results in localized eruptions that can create volcanic islands, such as those found in Hawaii.
• Evaluate the significance of decompression melting in understanding volcanic activity and its implications for geological hazards.
  • Decompression melting is critical for understanding how magma is generated and how it leads to volcanic eruptions. By studying this process, scientists can predict volcanic activity associated with mid-ocean ridges and hotspots. Additionally, recognizing how decompression melting contributes to magma composition can inform risk assessments for volcanic hazards. Knowledge about these processes helps develop strategies for monitoring eruptions and mitigating potential impacts on surrounding communities.

Related terms

Mantle:

The layer of the Earth located between the crust and the core, composed of silicate rocks that are semi-solid and capable of flow.

Magma: A molten mixture of rock-forming materials, gases, and crystals found beneath the Earth's surface, which can solidify to form igneous rocks.

Divergent Boundaries: Tectonic plate boundaries where two plates move apart from each other, creating new crust as magma rises to fill the gap.