Earth and Space Science - Plate Tectonics and Natural Hazards

The Earth is composed of four distinct layers: the inner core, outer core, mantle, and crust. The lithosphere (crust and uppermost mantle) is divided into tectonic plates that float on the semi-fluid asthenosphere.

Continental Drift Theory, proposed by Alfred Wegener, suggests that continents were once joined in a supercontinent called $Pangaea$ and have since drifted apart.

Plate movement is driven by convection currents in the mantle, where heat from the core causes magma to rise, cool, and sink in a continuous cycle.

Divergent Boundaries occur where plates move apart, leading to seafloor spreading at mid-ocean ridges and the formation of new oceanic crust. The rate of spreading is typically measured in $cm/year$.

Convergent Boundaries occur where plates collide. If an oceanic plate meets a continental plate, subduction occurs, forming deep-sea trenches and volcanic arcs. If two continental plates collide, they form fold mountains like the $Himalayas$.

Transform Boundaries involve plates sliding past each other horizontally. Friction causes pressure to build up, which is suddenly released as an earthquake (e.g., the San Andreas Fault).

Earthquakes release energy in the form of seismic waves: Primary waves ($P$-waves) are longitudinal and fast, while Secondary waves ($S$-waves) are transverse and slower. Surface waves cause the most destruction.

Volcanoes are formed by the movement of magma. High levels of silica ($SiO_2$) in magma increase viscosity, leading to more explosive eruptions in composite volcanoes compared to shield volcanoes.

Natural hazard mitigation involves monitoring seismic activity, building earthquake-resistant structures, and creating early warning systems for tsunamis caused by underwater tectonic shifts.