A team of scientists has created a new method for reconstructing the size of volcanic eruptions that have occurred long ago in the past, revolutionizing the study of previous eruptions and estimating hazards of future volcanic activities.
Geoscientists led by members from the University of South Florida (USF) developed an advanced numerical model that allows for reconstructing past eruption events - thousands of years ago. This is done by estimating the dimensions of umbrella clouds that help create large deposits of volcanic ash. Results of their study are published in the new Nature journal, Communications, Earth, and Environment.
Analyzing Volcanic Activities
Researchers note that in the case of large and explosive eruptions, it creates laterally spreading umbrella clouds up into the stratosphere. This phenomenon also encourages the transport of ash materials over large distances, covering larger areas of land when they settle down.
Current technology allows the direct observation of ash clouds. Meanwhile, past eruptions are only observed and analyzed based on the geological interpretation of their pyroclastic airfall deposits. These are rock and ash pieces ejected into the air - with their physical characteristics giving clues on the behavior of the volcanic eruption itself.
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Combining field techniques with numerical and statistical modeling, scientists can now extract information from the tephra deposits in characterizing and classifying past eruptions in accordance with the Volcanic Explosivity Index (VEI), one of the most common scales. However, as time passes, deposits can erode and make studying previous eruptions more challenging. Also, existing volcanic models do not account for volcanic eruptions that do not create vertical plumes and those that form laterally spreading umbrella ash clouds.
"The better we can reconstruct the nature of past eruptions from deposit data, the better we can anticipate potential hazards associated with future explosive eruptions," researchers argued in their paper.
Reconstructing Eruptions from Thousands of Years Ago
The new numerical model was used in understanding the nature of a volcanic eruption that occurred 2,500 years ago in Ecuador. Their proposal, an updated VEI scale that includes umbrella cloud dimensions, is made possible through their statistical and numerical models.
Researchers applied this new approach in the tephra deposits of a past Pululagua eruption, a now dormant volcano situated some 50 miles north of the Ecuadorian capital of Quito. The South American nation is now considered among the world's most hazardous nations because of its volcanoes. Pululagua last erupted 2,500 years ago and is now being used as a geobotanical reserve.
Using the new model, researchers showed that an erupted mass of between 1.5 to 5 X10 11 kilograms and an umbrella cloud radius of between 10 to 14 kilometers wide were created by the Pululagua eruption. The volcanic activity in the study also created an eruption column height of about 20 to 30 kilometers. With the values recovered, researchers argued that their modeling effort for this particular explosion was better modeled through a disk source and not the conventional estimates were taken from eruption column height.
Modern records show more than 1,500 potentially active volcanoes worldwide, plus volcanoes located underneath the world's oceans. In 2020 alone, there have been at least 67 confirmed eruptions from 63 different volcanoes around the world.
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