Built by a geologist
Volcanoes & Igneous Processes
Volcanoes & Igneous Processes Volcanoes are among Earth's most dramatic features — windows into the molten interior that continuously reshape our planet's surface. Magma vs. Lava - Magma : Molten rock below Earth's surface - Lava : Molten rock that has reached the surface - Same material, different names depending on location How Magma Forms Rock doesn't melt easily. Three mechanisms create magma: 1. Decompression melting : Rising mantle rock experiences less pressure and melts mid-ocean ridges, hotspots 2. Flux melting : Water released from a subducting plate lowers the melting point of overlying mantle rock subduction zones 3. Heat transfer : Hot magma heats surrounding rock enough to melt it contact melting Types of Volcanoes | Type | Shape | Eruption Style | Example | |------|-------|---------------|---------| | Shield | Broad, gently sloping | Effusive flowing lava | Mauna Loa, Hawaii | | Stratovolcano | Steep, conical | Explosive + effusive | Mount Fuji, Mount St. Helens | | Cinder cone | Small, steep | Mildly explosive | Parícutin, Mexico | | Caldera | Large depression | Catastrophic eruption | Yellowstone, Crater Lake | Eruption Style Depends on Magma Composition - Mafic magma basaltic : Low silica, low viscosity, hot 1200°C → flows easily, gentle eruptions - Felsic magma rhyolitic : High silica, high viscosity, cooler 800°C → traps gas, explosive eruptions - Intermediate magma andesitic : Between the two → mixed eruption styles Volcanic Hazards - Pyroclastic flows : Superheated clouds of gas, ash, and rock traveling 100+ km/h - Lahars : Volcanic mudflows that can travel tens of kilometers - Ashfall : Can collapse roofs, contaminate water, and disrupt aviation - Lava flows : Destructive but usually slow enough to evacuate - Volcanic gases : CO₂, SO₂, and H₂S can be lethal in confined areas Intrusive Igneous Bodies Not all magma reaches the surface. Underground, it forms: - Batholiths : Massive bodies 100 km² like the Sierra Nevada - Dikes : Sheet-like bodies that cut across existing rock layers - Sills : Sheet-like bodies that intrude parallel to existing layers - Laccoliths : Dome-shaped intrusions that push up overlying rock