A volcano can erupt in different ways. Scientists distinguish between “red” and “gray” volcanism. Red volcanism produces glowing lava effusively, in the form of lava fountains, lava flows, and lava lakes. Gray volcanism, on the other hand, is explosive and generates ash clouds that can rise all the way into the stratosphere.
There are several different eruption types or styles exhibited by volcanoes. Some of the most common eruption styles include:
Hawaiian Eruption: This type of eruption is characterized by the effusive flow of low-viscosity basaltic lava. Lava fountains and lava flows are common in Hawaiian eruptions. The lava flows can extend over long distances, and the eruptions are generally non-explosive.
Strombolian Eruption: Strombolian eruptions are characterized by frequent, moderate explosions. These eruptions produce incandescent lava fragments that are ejected into the air, creating a distinctive “Strombolian” fire fountain. The lava fragments fall back near the vent, building up cinder cones.
Vulcanian Eruption: Vulcanian eruptions are more explosive than Strombolian eruptions. They produce thick and viscous lava that can lead to the formation of volcanic domes. Vulcanian eruptions often generate ash plumes and pyroclastic flows.
Plinian Eruption: Plinian eruptions are highly explosive and can reach great heights in the atmosphere. These eruptions are characterized by the rapid expulsion of large amounts of gas, ash, and volcanic debris. Plinian eruptions often lead to the formation of volcanic columns and can cause significant ashfall and widespread effects.
Phreatomagmatic Eruption: Phreatomagmatic eruptions occur when magma interacts with water. This can happen when a volcano is submerged in a lake or the sea, or when groundwater comes into contact with hot magma. The water rapidly turns to steam, leading to violent explosions that produce ash and steam.
Submarine Eruption: Submarine eruptions occur underwater, and the erupted materials can build submarine volcanoes or lead to the formation of new volcanic islands when the erupted materials reach the surface.
Surtseyan Eruption: Surtseyan eruptions are a specific type of phreatomagmatic eruption that occurs in shallow marine or coastal environments. These eruptions produce columns of steam and ash that create a characteristic tuff ring.
These are some of the primary eruption styles observed in volcanoes. Each style is influenced by the composition of the magma, the presence of water or other volatiles, and the tectonic setting of the volcano.
Volcanic Explosivity Index (VEI)
The Volcanic Explosivity Index (VEI) is a scale used by volcanologists to measure the size and intensity of volcanic eruptions. It works a bit like the Richter scale for earthquakes but focuses on eruptions.
The VEI ranges from 0 to 8:
VEI 0 – Non-explosive eruptions, such as gentle lava flows (e.g., typical Kīlauea eruptions).
VEI 1–2 – Small to moderate explosive eruptions, producing ash columns up to a few kilometers high.
VEI 3–4 – Strong eruptions with significant ash plumes (up to 25 km high) and widespread fallout.
VEI 5 – Major eruptions, like Mount St. Helens in 1980, with ash spreading over large areas.
VEI 6 – Very large eruptions, such as Krakatoa in 1883, affecting global climate.
VEI 7 – Super-colossal events, like Tambora in 1815, which caused the “Year Without a Summer.”
VEI 8 – The rarest, most massive “super-eruptions” (e.g., Yellowstone ~640,000 years ago).
The VEI takes into account:
- The volume of erupted material (lava, ash, pumice).
- The height of the eruption column.
- The duration of the eruption.
- The qualitative description (gentle, explosive, cataclysmic).
Since the scale is logarithmic, each step represents roughly 10 times more erupted material than the previous one.
The VEI is closely related to the eruption style. Low VEI eruptions (0–1) are usually effusive, producing slow-moving lava flows with little or no explosive activity, like those at Kīlauea. Moderate VEI eruptions (2–3) are Strombolian or Vulcanian, with intermittent bursts of ash and lava that form small plumes. Higher VEI eruptions (4–5) are Plinian, generating towering ash columns and widespread tephra fall. At VEI 6 and above, eruptions are ultra-Plinian or cataclysmic, releasing enormous amounts of material, sometimes collapsing calderas and affecting global climate.