Assistant Professor of Climate Science Sally Warner recently authored an article in The Conversation magazine concerning the physical science underpinning the formation of waves and tsunamis.
This article was in response to the recent eruption of the underwater volcano Hunga Tonga-Hunga Ha’apai located within the island system making up the southern Pacific nation called Tonga.
According to The Associated Press, the initial reports of damage were difficult to assess due to the loss of internet on the island system. A recent New York Times article details witness reports and estimates of damage. The ashes from the volcanic explosion were spouted thousands of feet into the air. A four-foot tsunami wave from the explosion drastically impacted Tonga’s capital, Nuku’alofa.
Although Tonga is a remote southern Pacific nation, the sound from the volcanic explosion was reported to have been heard in the eastern coast of New Zealand, located approximately 1,100 miles southwest of Tonga.
The U.S. response to the news of the tsunami urged residents of the west coast, Alaska, and Hawaii to move far from the coastal front and onto higher ground. The Japanese meteorological agency reported that waves from the impact had reached parts of Japan’s Pacific coast.
As of now, the estimated death toll from the tsunami is low, however Warner writes that many people are still missing and the true scope of damage remains elusive.
The Hunga Tonga-Hunga Ha’apai underwater volcano had been mostly inactive for several years, but had intermittently began activity around Jan. 3, according to a report by the Smithsonian Institution’s Global Volcanism Program.
Warner writes about the physics behind how tsunami waves are generated and how they are different from normal wind-generated waves. According to the article, most waves are regulated by the movement of various air masses and the tidal fluctuations from the lunar cycle.
Tsunamis on the other hand are created by a different mechanism: rather than displacing water at the upper surface of the ocean, the tsunami force generated displaces water that extends through the entire depth of the ocean. Warner uses the analogy of someone blowing on the surface of water at a swimming pool in contrast to someone jumping in, writing, “The cannonball dive displaces a lot more water than blowing on the surface, so it creates a much bigger set of waves.”
Another key difference between tsunamis and wind-generated waves are the speed at which the waves are able to travel. While wind-generated waves travel about 10 to 30 miles per hour, tsunami waves can travel hundreds of miles per hour. For the Hunga Tonga-Hunga Ha’apai volcano, the speed of the wave calculated was about 440 miles per hour.
Tsunami waves are significantly more destructive than wind-generated waves because the ocean floor rises closer to the coast of a body of land. This causes the waves to be pushed up to taller heights, often capable of enveloping entire towns.
Warner writes that while tsunamis can be devastating, they are not nearly as much of a surprise now. This is credited to a system of bottom-pressure detecting buoys called DART-buoys which can detect the presence of tsunami waves and alert the governmental agencies to communicate early warnings.
Warner writes, “Tsunamis are one of my favorite topics to teach my students because the physics of how they move is so simple and elegant.” Her expertise lies in the interconnection between small-scale water turbulence in oceans and their influence on global phenomena such as El Niño and climate change.
