Volcanoes and Plate Tectonics

Volcanoes and Plate Tectonics

• Volcanoes are openings in the Earth's crust that allow molten lava, ash, and gases to escape.
• Form at tectonic plate boundaries and hotspots, where geological activity is concentrated.

Learning Objectives

• Define plate tectonic theory and its relationship to geological features.
• Understand processes shaping the Earth’s crust, including volcanoes and earthquakes.
• Explore methods to mitigate damage from geological phenomena.

Plate Tectonic Theory

• Explains formation and movement of geologic features through tectonic processes.
• Proposed by Alfred Wegener, who suggested all landmasses once formed a supercontinent called Pangaea.
• Earth's lithosphere consists of tectonic plates that float and interact.

Structure of the Lithosphere

• Lithosphere: Outermost layer combining the crust and upper mantle, approximately 80 km deep.
• Crust: Composed of rocks and sediments, 50 km deep with a density around 2.6 g/cm³.
• Two types of crust:
  • Continental crust: Thicker, less dense.
  • Oceanic crust: Denser, relatively thinner.

Types of Plates

• Major Plates include North American, South American, Eurasian, Pacific, Indo-Australian, African, and Antarctic.
• Smaller plates include Philippine, Caribbean, Cocos, Nazca, Scotia, Juan de Fuca, and Arabian plates.

Geological Processes

• Most earthquakes occur along plate boundaries, with varying strengths from shallow to destructive.
• Earthquakes can be triggered by plate collisions, rifting, or slip movements, releasing seismic waves.
• Volcanoes predominantly located at plate margins and in subduction zones; categorized as active, dormant, or extinct.

Mountain Formation

• Mountains arise from tectonic plate movements; some underwater, others on land.
• Notable contributions from Charles Wyville Thomson, who discovered the Mid-Atlantic Ocean Ridge, and Harry H. Hess, a proponent of seafloor spreading.

Key Concepts

• Primary and secondary seismic waves travel through Earth’s interior, while surface waves affect areas above ground.
• Volcanic arcs formed from magma accumulation are mostly found in the Pacific Ring of Fire, highlighting the dynamic nature of Earth's surface.