When you imagine volcanic
hazards, you might think of dramatic scenes of lava flows inundating
neighborhoods, such as the 2018 lava flows in Hawaii. The thing is, not all
hazardous volcanoes have people living on them. In fact, some of them are
erupting, growing, and collapsing underwater, yet can still pose a significant
hazard to people. Displaced water due to submarine landslides are capable
of producing hazardous water conditions,
including tsunamis. GPS equipment and satellite imagery make it relatively easy
to continuously monitor changes in volcanoes above the ocean. However, it’s a
much different story for volcanoes below the ocean’s surface, since satellite
images cannot be taken and GPS signals cannot transmit through water. This obstacle makes collecting continuous
real-time data about how these underwater features are changing almost
impossible. Instead we rely on periodically-deployed unmanned submarines to
create seafloor maps using lasers (Figure 1). This process is called
bathymetric surveying. These surveys are expensive to conduct, time-intensive,
and may require scientific equipment that is difficult to acquire. This means
that often many years pass before a new set of data can be collected.
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| Figure 1: Figure 3 from Allen et al. (2018) showing a 3D projection of a bathymetric map collected at a set of caribbean underwater volcanoes. The numbers mark the locations of features related to the volcano including: (1) collapse features, (2) Kick ‘em Jenny volcanic cone, (3) Kick-‘em-Jack volcanic cone, and (4/5) volcanic debris. |
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| Figure 2: Map showing the the location of Kick ‘em Jenny with a red pin (Google Maps, 2018). |
Kick ‘em Jenny (Figure 2) is an underwater volcano in the Caribbean that is thought to be named by sailors who noticed that the waters around it were often quite rough, presumably due to the changing landscape of the seafloor. Researchers (Allen et al., 2018) investigated the modern history of the underwater volcano by comparing the bathymetric data (i.e. underwater elevation) from 1984, 2003, 2013, 2016, and 2017 in an effort to identify possible risk. They wanted to identify where and how regions of the volcano were growing or collapsing. They did this by looking at the difference between datasets to isolate areas that had changed and measure how much change had occurred.
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| Figure 3: Figure 5 from Allen et al. (2018) showing areas where the volcano grew (red) and areas where the volcano experienced collapse or landslides (blue) between each timestep. |
Their results (Figure 3) allowed them to determine whether or not Kick ‘em Jenny was likely to produce a significant tsunami event. They did this by figuring out approximately how much material has been moved during landslide events, which allowed them calculate how large of an impact those landslides could have at the surface of the water. They also determined a worst-case scenario for the largest landslide event that the volcano is capable of producing and calculated the size of the waves that such an event would produce. Their results came with good news for people living on the Caribbean islands: it would actually be unlikely for this volcano to produce waves at the water's surface that could pose a significant threat to people on land. In their worst-case scenario, their models showed that the nearby island of Grenada could possibly experience waves as high as 6 meters tall, and waves would be around 1 meter tall by the time they reached Puerto Rico. This means that Kick ‘em Jenny doesn’t pose a widespread tsunami threat, but lower elevation areas along Grenada’s west coast could be affected, particularly near beaches along the southwest portion of the island. The largest event that they have evidence for in modern history is about 30x smaller than the worst-case scenario and so they determined that volcanic hazard monitoring should focus on how tumultuous waters might impact ships traveling through the region.
References
Allen, R. W., et al. "30
Years in the Life of an Active Submarine Volcano: A Time‐Lapse Bathymetry Study
of the Kick‐'em‐Jenny Volcano, Lesser Antilles." Geochemistry, Geophysics, Geosystems 19.3 (2018): 715-731. https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GC007270
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