Hawaii’s Kilauea volcano erupting in 2018
U.S. Geological Survey via Getty Images
Geologists will need to rethink their theories about where volcanic eruptions in areas like Iceland and Hawaii come from now that they know the plumes of rock that feed them are far cooler than they had assumed.
Volcanic zones along the margins of tectonic plates are not linked to volcanic hotspots. Hot plumes of rock from the Earth’s mantle are believed to supply them with energy and material as they rise and grow.
Some of these hotspots, however, have been found to be fed by relatively cold material by Carolina Lithgow-Bertelloni and her colleagues at the University of California, Los Angeles, suggesting that other processes may be at play.
“We’re not saying these aren’t hotspots; we’re saying yes, they are, but there are different mechanisms that help them rise,” explains Lithgow-Bertelloni. To paraphrase, “you may still have slightly warm material that comes up, but it’s not coming up all from depth and all in the same way; it’s being aided by other processes in the mantle.”
It’s challenging to estimate how hot the ground is beneath active volcanoes. The upper mantle has a depth of between 250 and 600 kilometres, making direct exploration impossible. Using a model of the rock composition, Lithgow-Bertelloni and her team extrapolated temperatures by measuring the velocity of seismic waves passing through the ground beneath volcanic hotspots.
Scientists compared these areas to those at tectonic boundaries, where volcanic zones are typically cooler than those on the ridges themselves. In conventional theory, for plumes to ascend, they must be between 100 and 300 degrees Celsius hotter than the ridges.
However, more than half of the hotspots analysed were only about 100°C hotter than the surrounding ridges. Almost one-sixth of the hotspots were barely warm, with temperatures no more than 36 degrees Celsius above the surrounding ridges.
You wouldn’t anticipate low temperature excesses, says Oliver Shorttle of Cambridge University, because that would suggest there isn’t enough energy to cause the object to bloat and rise.
According to the study’s findings, cold and hot hotspots may originate from different regions of the mantle due to their varying helium isotope ratios. The evolution of the Earth’s tectonic plates may be revealed by studying the characteristics of volcanic hotspots and the material beneath them.
FAQs
Q1: What are volcanic hotspots?
A1: Volcanic hotspots are areas with concentrated volcanic activity, often occurring away from tectonic plate boundaries.
Q2: What supplies energy and material to volcanic hotspots?
A2: Hot plumes of rock from the Earth’s mantle are believed to supply energy and material to volcanic hotspots.
Q3: How do the recent findings challenge existing theories?
A3: Recent research suggests that some volcanic hotspots are fed by relatively cooler material than previously assumed, indicating the involvement of different processes.
Q4: What mechanisms aid the rise of these cooler plumes?
A4: Cooler plumes of rock are aided by processes in the mantle other than solely rising from depth.
Q5: How were the temperatures beneath volcanic hotspots estimated?
A5: Scientists used a model of rock composition and measured seismic wave velocities to extrapolate temperatures beneath volcanic hotspots.
