Volcanic Eruptions

• Volcanoes show a range of eruption types, from steam explosions to the ejection of material causing ground collapse above the magma chamber.
• Eruptions can involve fluid lava flows or catastrophic events ejecting ash plumes high into the atmosphere.

Classifying Volcanic Eruptions

• Geologists use different methods to describe and classify eruptions, with each method focusing on different aspects of eruptive events.
• Eruption type is based on whether the eruption is steam-driven, involves magma emissions, or occurs because of the interplay between water and hot magma.
• The Volcanic Explosivity Index (VEI) measures the magnitude and intensity of explosive eruptions, considering magma volume and eruption column height.
• Eruption style classification describes the strength of eruptions by drawing on well-known volcanoes' classic eruption characteristics.
• Volcanic eruptions can be magmatic, phreatic, or phreatomagmatic.
• Magmatic eruptions involve lava or tephra ejection from a magma source and vary significantly in intensity, magnitude, and eruption rate.
• Magmatic eruptions are classified as effusive (dominated by passive lava emission) or explosive (dominated by fragmental pyroclastic material eruption).
• A volcano can have phreatic and Plena eruptions, while others only have one characteristic type.

Types of Volcanic Eruptions (USGS Classification)

• Phreatic eruptions happen when the steam results from cold groundwater and hot rock or magma, and only fragments of preexisting solid rock are expelled, these are "generally weak."
• The 2020 Taal Volcano and the Mayon Volcano in 2018 are examples of Phreatic eruptions.
• Plinian eruptions, are the most powerful and eject viscous lava, gas-rich magma, and pumice, and can last from hours to months.
• The 1991 Pinatubo explosion in Zambales, the second-largest eruption of the 20th century, was a strong plinian eruption.
• Pelean eruptions, are named after Mt. Pelee in Martinique, and can create domes and hot ash avalanches down a volcano's sides.
• Pelean eruptions produce gas, dust, ash, and lava fragments but tephra spreads less than from plinian eruptions, the Mayon Volcano explosion in 1968 is an example.
• Hawaiian eruptions, produce volcanoes with high magma temperatures, low viscosity lava flows, and low gas content.
• They can start along the fissures, examples of locations include along volcanoes or linear vents which can be fissure type or central type eruptions.
• Fissure eruptions emit incandescent lava, and central-vent eruptions shoot blazing lava high into the air, an example of the Hawaiian eruption happened in 1959 in the Kilauea Iki Crater of Kilauea Volcano in Hawaii.
• Strombolian eruptions, named after Italy's Stromboli volcano, blast solidified lava and rocks to tens or hundreds of feet, forming luminous arcs, and are created from molten lava bursts from the volcano's crater.
• Lava and magma have higher viscosity and activities last to a few years, the Paricutin Volcano in Mexico is an example.
• Vulcanian eruptions, named after Vulcano Island in Italy where an ash-filled gas explosion from the crater creates a dense cloud, which can be gray or black.
• Hawaiian and Strombolian eruptions, the rock fragments are more widespread but that doesn't necessarily mean higher amounts.

Volcanic Explosivity Index (VEI)

• Volcanic eruptions can range from gas emissions to quiet lava flows to explosions that devastate miles, the 1980 eruption of Mount St. Helens is an example.
• the 1912 Novarupta eruption was 30 times bigger by volume than the St. Helens one.
• The Volcanic Explosivity Index (VEI) measures the size of explosive eruptions by magnitude and intensity, on a scale from 0 to 8.
• The Volcanic Explosivity Index (VEI) is similar to the Richter scale

Information in the VEI Table

• On the VEI scale, each interval on it shows a ten-fold increase in the size of an eruption.
• Effusive Hawaiian-style eruptions rate zero VEI and supervolcano eruptions rate eight VEI.
• Calculations are based on volume of magma erupted (magnitude) and the eruption column height.
• The height of the eruption column directly relates with eruption intensity as well as the rate of eruption.
• This is not helpful useful for effusive eruptions of lava since the scale calculates based on volume of tephra erupted and height of eruption column height.
• The index assigns a one qualitative word like catastrophic, which includes traditional classification of other eruptions, based on classic eruptions.
• Categories are derived from eruption styles of volcanoes, but are typically described as a poor definition as a single eruption may include separate differences.
• The classification is widely popular and and applied in volcanological references, and used to describe the eruptions of national park volcanoes.