Glossary term
Alert level
Volcanoes · earthquake & volcano glossary
What is Alert level?
The official status an agency assigns to a volcano (for example PHIVOLCS Alert Levels 0–5). It reflects current unrest and the likelihood of eruption, and is the strongest input to QuakeGlobe's probability estimates.
Volcanoes →Related terms
Volcanic Explosivity Index (VEI)A 0–8 logarithmic scale of eruption size based on erupted volume and plume height. VEI 0 is gentle effusion (lava flows); VEI 5+ are major explosive eruptions like Pinatubo (VEI 6, 1991).Volcanic tremorContinuous ground vibration caused by moving magma or gas, as opposed to the discrete jolts of tectonic earthquakes. Sustained tremor often precedes eruptions.CalderaA large basin formed when a volcano's summit collapses into the emptied magma chamber after a big eruption. Taal and Yellowstone sit in calderas.Moment magnitude (Mw)The modern measure of an earthquake's size, based on the area of the fault that slipped and how far it moved. It replaced the original Richter scale for medium and large events because Richter saturates (stops increasing) for the biggest quakes. The scale is logarithmic: each whole number is about 10× more shaking amplitude and ~31× more energy.Richter scale (ML)The original 1935 local-magnitude scale. Still widely cited in the media, but agencies now report moment magnitude for most events because it stays accurate for large earthquakes.Intensity (MMI)How strongly shaking is felt at a given place, on the Modified Mercalli Intensity scale (I–XII). Unlike magnitude — one number per earthquake — intensity varies with distance, depth, and local soil. A single quake produces many intensity values.
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