On 3 May 2018, lava burst through the foot of Kīluaea, Hawaii’s most active volcano. The eruption continued for months, consuming hundreds of homes as molten rock flowed downhill into the Pacific Ocean. Now, a new study characterizes how such events—known as effusive eruptions—erode the volcanic conduit that magma flows through over time. This finding could help scientists better understand how Kīlauea and similar volcanoes wreak havoc.
Unlike violent, explosive eruptions like the 1980 Mount St. Helens event, effusive eruptions occur when lava simply pours or flows out of fissures and cracks around a volcano. To predict how long an effusive eruption like Kīlauea’s will last and how far the lava will travel, scientists need to know the effusion rate, or the rate at which hot, molten rock is flowing out. Many variables affect this rate, including how fast the magma reservoir below empties and refills and the properties of the rock through which magma moves. The rate of magma refill can also affect how fast volcanic conduits erode, a factor that few studies have examined before.
To address this knowledge gap, Aravena et al. created a computer model that simulates magma flowing upward through a 10-kilometer-long vertical dike. The model includes factors such as fluid shear stress—the stress generated by two surfaces rubbing against one another—and elastic deformation. Next, they ran simulations of two different scenarios: one in which the magma reservoir feeding the volcanic conduit simply emptied out without refilling and another in which magma flowed up from below, refilling the reservoir.
They found that the relative balance between conduit widening, elastic deformation, and the decreasing trend of magma reservoir overpressure controls the evolution of effusion rate and eruption duration. When a magma reservoir is replenished, it causes a sharp increase in magma reservoir pressure and in erosion rate along the conduit. These changes could even lead to a 30% faster effusion rate at first, but as the conduit in the model widens and pressure in the magma reservoir decreases, effusion rate is expected to gradually decline. Given the difficulty of measuring the activity of magma reservoirs directly, such data could help scientists better understand Kīlauea and other effusive eruptions, the team writes. (Geophysical Research Letters, https://doi.org/10.1029/2018GL077806, 2018)
—Emily Underwood, Freelance Writer