Geology: Magma and Its Properties

Magma

• Molten rock located beneath the Earth's surface, specifically in the melted mantle rock and oceanic plate.

Magma and Lava

• Both are molten rocks.
• Magma is found in the magma chamber of a volcano.
• Lava is found on the Earth's surface after a volcano erupts.

Magmatism

• The formation and movement of magma under the Earth's crust.

Where Magma Forms

• Asthenosphere: A hot, mobile layer of partially molten rock within the Earth's upper mantle.
• The formation and movement of magma occurs in the asthenosphere.

Composition of Magma

• Made up of silicate minerals, primarily feldspar and quartz.
• Contains dissolved gases, including water vapor, carbon dioxide, hydrogen sulfide, and sometimes hydrochloric or sulfuric acid.

Formation of Magma

• Geothermal gradient: The rate of increasing temperature with respect to increasing depth in the Earth's interior.
• Partial melting: Rocks have different mineral compositions and therefore different melting points. When hot rocks start to melt deep in the Earth, some minerals melt while others stay solid.
• Decompression melting: The upward movement of the Earth's mostly solid mantle (through convection) causes a decrease in pressure, resulting in a lower melting point and the formation of magma.
  • Occurs at divergent boundaries where tectonic plates separate.
  • Occurs at mantle plumes, columns of hot rock rising from the Earth's core to the crust.
• Flux melting: Water or carbon dioxide added to rock causes the rock to melt at lower temperatures.
  • Occurs around subduction zones where water from the subducting seafloor lowers the melting temperature of the mantle.

Viscosity

• A measure of a fluid's resistance to flow.
• Magma with high silica content has higher viscosity and flows less easily than magma with low silica content.
• Dissolved gases can also influence viscosity.

What Happens to Magma After It Forms?

• Cooling and Solidification: As magma rises and cools, it crystallizes into igneous rocks.
• Volcanic Eruptions: If magma reaches the surface, it erupts as lava.
• Intrusive Igneous Rocks: Magma can solidify underground, forming intrusive igneous rocks like batholiths and dikes.

Explore the fascinating world of magma, the molten rock beneath the Earth's surface. This quiz covers its formation, composition, and the differences between magma and lava. Test your knowledge of geological processes and the asthenosphere!