Why The Russian Earthquake Caused A Weaker Tsunami Plus 4 Other Facts
They Are Not Weather Phenomena
As a meteorologist, I am often asked about tsunamis by the media and the public. I think the word 'tsunami' sounds meteorological to many people. However, tsunamis are geologic and oceanographic hazards. What is a tsunami anyhow? The NOAA Tsunami Warning Center website stated, 'It is a series of extremely long waves (multiple waves tens-to-hundreds of miles between crests) caused by a large and sudden displacement of the ocean.' That displacement of the ocean is typically caused by an earthquake, landslides or volcanic eruption. The site went on to say, 'Tsunamis radiate outward in all directions from the point of origin and can move across entire ocean basins. When they reach the coast, they can cause dangerous coastal flooding and powerful currents that can last for several hours or days.'
How This Tsunami Ranks Historically
The memes have already started on social media as many people perceived that the tsunami threat did not match the level of warnings. I am of the 'better safe than sorry' mentality when it comes to hazards, but I digress. Previous strong earthquakes in that region have generated significant tsunami hazards. Because of its location in the ring of fire, the region is known for earthquakes. In fact, the fifth strongest earthquake in history (magnitude 9.0) happened there in 1952. Two weeks ago, Kamchatka had a magnitude 7.4 earthquake, according to Science News. Preliminarily, this earthquake ranks as the sixth strongest of all time, according to the BBC.
In this seismic hot spot, the dense Pacific Plate is trying to thrust itself beneath the North American Plate. Geologists have referred to this particularly tremor as a 'megathrust earthquake." Earthquakes Canada website defined that type of seismic activity as, 'A very large earthquake that occurs in a subduction zone, a region where one of the earth's tectonic plates is thrust under another.'
Why The Recent Tsunami Was Relatively Weak
A tsunami certainly happened, but why was it relatively muted? Gauges in Hawaii measured wave heights in the 4 to 5 feet range. U.S. Geological Survey expert Rich Briggs told Science News writer Nikk Ogasa, 'To push a big wave all the way across the Pacific, you really need a monster source, and this one is just knocking on the door of that.' Other factors that may have suppressed the tsunami include seafloor characteristics, coastline attributes, and the interaction of waves.
University of Southhampton expert Lisa McNeill told the BBC, "The height of the tsunami wave is also affected by local shapes of the seafloor near the coast and the [shape]
of the land where it arrives." Some studies have shown that if the quake is at shallow depth the tsunami is larger than if the shock is deeper. McNeill also said that with this earthquake, warning models may have been conservative with the depth information.
They Don't Look Like Large Breaking Waves At The Coast
According to NASA, 'Between 1998 and 2017, the global death toll from tsunamis exceeded 250,000, according to the WHO. 227,000 of those deaths came from the devastating Indian Ocean tsunami in 2004.' Perceived risk from a tsunami can vary because of dangerous misperceptions about them.
I often use the visual of throwing a rock in a pond and watching waves ripple away from the center as an analogy to a tsunami. However, with a tsunami, the waves are traveling beneath the water. It becomes apparent when it reaches a coastline. NOAA noted, 'When a tsunami reaches the coast, it may look like a fast-rising flood, or a wall of water (bore). Its appearance may differ at different points along a coast. It will not look like a normal wind wave.' One dangerous misperception is that tsunamis will look like large breaking waves seen at surf competitions. That misperception is also associated with hurricane storm surge. NOAA cautioned, 'Sometimes, before the water rushes on land, it will suddenly recede, showing the ocean floor, reefs, and fish like a very low, low tide.'
Multiple Observation Systems And Models Track And Predict Tsunamis
So how do scientists track and predict tsunamis? The Tsunami Warning Centers uses seismic networks to determine magnitude, depth, location, and other earthquake characteristics. Water-level networks such as the Deep-ocean Assessment and Reporting of Tsunami (DART) system and a system of coastal water-level stations detect changes in water level. Satellites with special altimetry instruments can also detect subtle changes in wave heights from space.
In the same way that meteorologists like me use numerical models to predict changes in the atmospheric fluid in time (a forecast), scientists feed information about earthquake magnitude, depth, and location into forecast models to predict tsunami motion across the ocean and potential coastal impacts. Information from seismic and water-level networks are important to the forecast models. For more information on the warning, watch and advisory messaging process, the NOAA Tsunami Warning Center FAQ page is a great resource.
There Are Meteotsunamis, But They Are Different
By the way I joked earlier about people asking meteorologists about tsunamis. There is actually something called a meteotsunami. I wrote about one in Florida many years ago. Meteotsunamis are caused abrupt jumps in atmospheric pressure often associated with strong weather fronts or other mesocale storm systems.
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