Bob White on How Magma Moves Through the Crust
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Bob White and his research group use highly sensitive seismometers to measure seismic waves from controlled sources and earthquakes. He uses this data to learn about the structure and behavior of the lithosphere. In the podcast, White describes how he obtained an unprecedentedly detailed real-time view of the lateral movement of melt about 6 km below the surface of Iceland just before it erupted.
White is Emeritus Professor of Geophysics in the Department of Earth Sciences at the University of Cambridge. In the image, he is connecting a battery for a broadband seismometer in the Highlands of north Iceland.
Podcast Illustrations
Images courtesy of Bob White unless otherwise indicated.
2014 Bárðarbunga-Holuhraun Rifting Event
Map of the area White and his team studied leading up to the 2014 eruption just before the laterally flowing melt reached the Holuhraun volcano. Each of the main segments (S1 to S4) became seismically quiet once a new segment had intruded beyond it, producing the step-like propagation of seismicity.
Animation showing the progression of seismicity over a 13-day period leading up to the 2014 eruption at Holuhraun in central Iceland described in the podcast. Each dot in the animation represents a microquake (of magnitude ~ 1) detected during the 48-km lateral migration of magma at a depth of about 6 km. The dot colors indicate the day each quake occurred and help visualize the forward movement of the melt.
Propagation of seismicity through time is revealed in this plot of the earthquake locations measured in distance along the dike versus time. The phases where the melt propagated are shaded grey, the eruption periods are shown in peach, and the fissure location is orange. The plot shows the stop-start propagation of the dike as well as the way that seismicity ceases once an underground channel has been opened up.
Ágústsdóttir, T., et al. (2016), Geophys. Res. Lett., 43, doi:10.1002/2015GL067423
Diagrammatic cross-section through the Bárðarbunga volcano caldera and the dike along which the melt flowed before erupting. The detected earthquakes are colored by depth, from shallowest (yellow) to deepest (purple).
Ágústsdóttir, T., et al. (2019), Journal of Geophysical Research, Solid Earth, 124, 8331
Fire fountains captured about a month after the start of the 2014 Holuhraun eruption that followed the 48-km lateral movement of the melt observed by White and his team. As mentioned in the podcast, being low in silica content, the lava here has a much lower viscosity than that erupting from the volcanoes above a subduction zone. The fountains are about 100 m high.