As a planetary geologist, I’m more well versed in ways of destroying life than in creating it. This next story is your daily reminder that the Universe is trying to kill us, and it doesn’t even need rocks from outer space to do so. No, no. The Universe can rely on mother Earth to do her fair share.

When I taught a natural hazards class, one of the things I had to explain to my students were the hazards that go along with earthquakes. After all, I live in earthquake country, but beyond the normal shaking and rolling land waves we get here in California, there is one type of hazard our quakes aren’t generally responsible for: tsunami. These deadly events are usually the result of subduction earthquakes, those ones where one tectonic plate is going under another plate.

Subduction earthquakes are common around the Pacific Ocean in what is known as the Ring of Fire. The same plate interactions that cause those volcanic arcs we talked about a couple of weeks ago also come along with massive quakes. And when one of those happens, the upward thrust of the topmost plate causes water to also be displaced upward. That water has to go somewhere to keep everything even, and like ripples in a pond, it spreads out from that point of origin, creating a tsunami.

As the tsunami approaches the shoreline, the water pulls back from the show while the wavefront gets compressed in the shallower depths, building up what we think of as a wall of water. In the 2011 Tōhoku earthquake, the wave height at the shore was on the order of 10 meters, causing massive amounts of destruction along the coast and even farther inland. The water will keep moving, and because these huge ripples bounce, they’ll go back and forth for a while. The 2004 Boxing Day tsunami occurred as a result of a quake off the coast of Sumatra, and over two hundred thousand people died as a result, in countries as far away from the epicenter as Kenya and Tanzania.

Unfortunately, we tend to learn lessons only when they are particularly harsh, and scientists realized that this extreme death toll was partially due to the lack of warning systems in place in the region in 2004. So they quickly increased the number of Deep-ocean Assessment and Reporting of Tsunamis or DART buoys in the region and created a network that now includes over 60 of the floating sensors. This includes twelve new buoys over the Kermadec Trench near New Zealand, which is a particularly fast-moving subduction zone and prone to frequent, high-magnitude earthquakes.

And they got to “witness” in the resulting data this year an extremely rare event: a triple tsunami as a result of three closely spaced, very large earthquakes, all over magnitude 7.0. These quakes occurred on March 5, 2021, off the coast of New Zealand, all within 1,000 kilometers and several hours of each other. Each quake spawned its own tsunami, and the buoys recorded the changes in the wave heights as each event passed by. Since the data is analyzed in real time, local authorities were able to keep the public informed of any pending threats and to cancel the warnings when the threat had passed. Because these buoys are in place, authorities canceled the alert more than four hours earlier than previously possible.

And these buoys don’t just save lives and time in the South Pacific. The tsunami generated by all these subduction earthquakes can travel swiftly across the Pacific and Indian Oceans, traveling at speeds in excess of 800 kilometers per hour and reach distant shores in countries like Chile and the United States. During that 2011 quake, several lives were lost in California, and the property damage in marinas along the coast was extensive. Here’s hoping for more buoys in more places to save more lives.

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