Measurement

VEI (Volcanic Explosivity Index)

"A logarithmic scale (0-8) used to measure the explosive magnitude of a volcanic eruption, similar to the Richter scale for earthquakes."

The Volcanic Explosivity Index (VEI) is the standard measuring stick used by volcanologists to quantify the power and magnitude of an eruption. Developed in 1982 by Chris Newhall and Stephen Self, it provides a way to compare the tiny “burps” of a daily volcano with the planet-altering cataclysms of the past. It is not determined by the destructive impact on humans, but by pure physical output.

How VEI is Calculated

The index is determined primarily by two factors:

  1. Volume of Ejected Material: How much tephra (ash, pumice, and rock) is thrown out? This is measured in cubic kilometers.
  2. Plume Height: How high does the eruption column reach into the atmosphere?

The scale ranges from VEI 0 (non-explosive) to VEI 8 (mega-colossal). Crucially, the scale is logarithmic from VEI 2 upwards. This means that a VEI 5 is 10 times larger than a VEI 4, and a VEI 6 is 100 times larger than a VEI 4.

The Scale Breakdown

  • VEI 0 (Effusive): Gentle lava flows with no explosion. The plume is less than 100m.
    • Examples: Kīlauea (Hawaii), Fagradalsfjall (Iceland).
  • VEI 1 (Gentle): Small, rhythmic explosions.
    • Examples: Stromboli (Italy), Mt. Etna (minor activity).
  • VEI 2 (Explosive): Columns 1-5 km high.
    • Example: Whakaari (2019), Mount Sinabung.
  • VEI 3 (Severe): Columns 3-15 km high. Significant local damage.
    • Example: Nevado del Ruiz (1985), Soufrière Hills (Montserrat).
  • VEI 4 (Cataclysmic): Columns 10-25 km high. Disruption to air traffic and regional climate.
    • Example: Eyjafjallajökull (2010), Mount Pelée (1902).
  • VEI 5 (Paroxysmic): Columns >25 km. Can produce global cooling.
    • Example: Mount St. Helens (1980), Mount Vesuvius (79 AD).
  • VEI 6 (Colossal): Columns >30 km. Major global climate impact (Volcanic Winter).
    • Example: Krakatoa (1883), Mount Pinatubo (1991).
  • VEI 7 (Super-Colossal): Events that change history.
    • Example: Mount Tambora (1815) - caused the “Year Without a Summer.”
  • VEI 8 (Mega-Colossal): Extinction-level events. Mass ejections >1,000 km³.
    • Example: Yellowstone (640,000 years ago), Toba (74,000 years ago).

Limitations

While useful, VEI only measures explosivity. It does not account for duration. A lava eruption (VEI 0) like the 2021 La Palma event can last for months and destroy thousands of homes, while a VEI 3 explosion might last only a few hours. Therefore, VEI is a measure of magnitude, not necessarily of hazard or risk.