Basalt

Definition

Basalt is a dark, fine-grained volcanic rock that forms from the rapid cooling of low-viscosity lava. It is the most abundant volcanic rock on Earth and primarily constitutes the oceanic crust, playing a crucial role in the formation of various landforms and features associated with different tectonic settings.

5 Must Know Facts For Your Next Test

1. Basalt typically forms at divergent plate boundaries and hot spots, where tectonic activity allows magma to rise and erupt onto the surface.
2. The composition of basalt is primarily mafic, meaning it contains a high percentage of iron and magnesium, which contributes to its dark color.
3. Basalt can create distinct geological features such as shield volcanoes, which are characterized by broad, gently sloping sides formed by low-viscosity lava flows.
4. When basaltic lava cools rapidly, it can form columnar jointing, resulting in unique structures like those seen at Giant's Causeway in Ireland.
5. Basalt is often found in vast oceanic plateaus and flood basalts, which are large areas covered by thick layers of basaltic lava that have erupted over millions of years.

Review Questions

• How does the formation of basalt relate to the processes occurring at divergent plate boundaries?
  • At divergent plate boundaries, tectonic plates move apart, allowing magma to rise from the mantle. This magma has low viscosity due to its mafic composition, which includes iron and magnesium. As it reaches the surface and erupts as lava, it cools quickly to form basalt. This process leads to the creation of new oceanic crust and various landforms associated with volcanic activity.
• Discuss how basalt influences the characteristics of shield volcanoes compared to stratovolcanoes.
  • Basalt significantly influences the structure of shield volcanoes by allowing for low-viscosity lava flows that spread out over large areas. This creates broad, gently sloping formations typical of shield volcanoes. In contrast, stratovolcanoes are built up from more viscous lavas, which tend to be andesitic or rhyolitic in composition. This results in steeper slopes and more explosive eruptions. Thus, basalt is a key factor in differentiating between these two types of volcanic structures.
• Evaluate the role of basalt in shaping volcanic landforms across different tectonic settings and its implications for understanding Earth’s geological history.
  • Basalt plays a vital role in shaping volcanic landforms across various tectonic settings, such as mid-ocean ridges where it forms new oceanic crust and hotspot islands like Hawaii. The unique characteristics of basaltic eruptions lead to distinct landforms such as shield volcanoes and flood basalts. Understanding how basalt interacts with tectonic processes helps scientists unravel Earth’s geological history, revealing patterns of plate movements and volcanic activity over millions of years, which have significant implications for both geological research and natural hazard assessments.

Related terms

Magma: Magma is molten rock located beneath the Earth's surface, which can cool and solidify to form igneous rocks like basalt when it erupts as lava.

Lava Flow: A lava flow is the movement of molten rock on the Earth's surface, which can create landforms like basalt plateaus when basaltic lava erupts and spreads over wide areas.

Tectonic Plates: Tectonic plates are large pieces of Earth's lithosphere that move and interact at their boundaries, influencing volcanic activity and the formation of basaltic landforms.