Earthquake
An earthquake is the shaking of the Earth's surface caused by a sudden release of energy in the Earth's lithosphere, which creates seismic waves. This energy release is usually due to the movement of tectonic plates.
- Primary Wave (P)
- Secondary Wave (S)
- Surface wave (L)
Volcanism
Volcanism is the process by which molten rock (magma), gases, and other materials erupt from the Earth's interior onto its surface. This phenomenon creates various landforms, most notably volcanoes.
Magma Generation: Deep within the Earth, intense heat and pressure cause rocks to melt, forming magma. This magma is less dense than the surrounding solid rock, so it begins to rise.
Magma Accumulation: As magma rises, it collects in chambers beneath the Earth's crust, known as magma chambers.
Pressure Build-Up: Gases are dissolved within the magma. As the magma rises and pressure decreases, these gases expand, increasing the pressure within the magma chamber.
Crustal Fracturing: When the pressure of the magma exceeds the strength of the overlying rock, it forces its way through existing cracks or creates new fractures in the Earth's crust.
Eruption: The magma, now called lava when it reaches the surface, along with gases, ash, and rock fragments, erupts through these openings, forming a volcano. The style of eruption (explosive or effusive) depends on the magma's viscosity and gas content.
Effusive eruptions (like those in Hawaii) involve runny, low-viscosity lava that flows relatively gently.
Explosive eruptions (like Mount St. Helens) occur with thick, high-viscosity magma that traps gases, leading to explosions.
Formation of Volcanic Landforms: As the erupted materials cool and solidify, they build up, forming various volcanic structures such as shield volcanoes, composite volcanoes (stratovolcanoes), cinder cones, and calderas.
Volcanism is closely linked to plate tectonics, often occurring at plate boundaries where plates converge (one slides under another) or diverge (move apart). It can also happen at "hotspots" within plates, where plumes of hot material rise from deep within the Earth's mantle.
