Earthquakes & Volcanoes

• A volcano forms when magma erupts as lava through a vent — composite (steep, sticky lava, explosive) vs shield (gentle, runny lava, frequent, calm) volcanoes.
• An earthquake is sudden, violent shaking caused by tectonic plates jolting free after getting stuck — the focus is underground, the epicentre is directly above it on the surface.
• About 90% of earthquakes and 75% of active volcanoes occur around the Pacific "Ring of Fire."
• The Earth has 4 layers: inner core → outer core → mantle → crust. The crust is broken into tectonic plates that move due to convection currents in the mantle.
• 4 types of plate boundary: divergent (constructive), convergent (destructive), collision, and transform (conservative) — each produces different hazards.
• Effects are split into primary (direct — e.g. ground shaking, lava flow) and secondary (knock-on — e.g. tsunami, liquefaction, fires).
• Impact severity depends on human factors (building quality, population density, preparation) and physical factors (magnitude, depth, distance from epicentre, geology).
• Living near volcanoes/earthquake zones brings opportunities too: fertile soil, tourism, geothermal energy, minerals, stronger building codes and research.
• Responses are short-term (aid, rescue) or long-term (building codes, monitoring, land-use planning, education/drills).
• Case studies: Nepal earthquake (2015) — collision boundary — and La Palma / Cumbre Vieja eruption (2021) — hot spot volcano.

Think of a volcano as a giant pressure-release valve for the Earth. Deep underground, molten rock called magma sits in a magma chamber. When pressure builds enough, it forces its way up through a main vent (sometimes with smaller secondary cones branching off) and bursts out onto the surface. The moment magma reaches the surface, we stop calling it magma and start calling it lava — same stuff, new name, just like "rain" becomes "puddle" once it hits the ground.

The magnitude of an eruption is measured using the Volcanic Explosivity Index (VEI) — an open-ended scale (like the Richter scale but for volcanoes). The most powerful eruption in recorded human history was Tambora in 1815, which scored a 7.

Volcanoes come in three "life stages":

Composite vs Shield Volcanoes

type type of lava