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This article was originally posted on RealClearScience.

The deadliest tsunami in world history struck southeast Asia on Boxing Day 2004 following a behemoth 9.1-magnitude earthquake. Several years later, in March 2011, another tsunami hit Japan, again following a 9.0-magnitude quake. It is not a surprise, then, that geophysicist Gerard Fryer considers earthquakes to be the most common cause of tsunamis. But, they are not the only cause. Landslides are the second most common cause, such as the ones that generated tsunamis in Lake Geneva and Doggerland, a now submerged region of land in the North Sea that once connected Britain to mainland Europe.

Relatively minor causes of tsunamis include volcanic eruptions and meteor strikes. Surprisingly, rare weather phenomena can trigger a tsunami, and new research concludes that it was an atmospheric perturbation that caused a series of meteorological tsunamis (“meteotsunamis”) that struck locations all over Europe in late June 2014. The oddest thing about the meteotsunamis is that they occurred during nice weather.

The figure above depicts three factors that conspired to cause the meteotsunamis: (1) Warm, dry air coming in from Africa at a height of ~5,000 feet (see first column); (2) A strong jetstream at ~16,000 feet blowing from the southwest (see second column); and (3) Atmospheric instability (see blue areas in third column). As this weather system moved eastward, so did the occurrence of meteotsunamis (see circles in third column).

The meteotsunamis, some as high as 3 meters (10 feet), hit coastal areas all over Europe. The authors propose that ocean waves generated by air pressure changes and amplified by resonance were to blame. They also suggest that tsunami warning systems should monitor not only earthquakes, but also freak weather conditions. That appears to be a very sensible idea.

Source: Jadranka Šepić, Ivica Vilibić, Alexander B. Rabinovich & Sebastian Monserrat. “Widespread tsunami-like waves of 23-27 June in the Mediterranean and Black Seas generated by high-altitude atmospheric forcing.” Scientific Reports 5, Article number: 11682. Published: 29-June-2015. doi:10.1038/srep11682