Last night, just before I went to bed, my friend and fellow writer at Victoria-Weather Anthony Dunkel told me to turn it ot CNN, where the video of the tsunami washing away parts of northeastern Japan was being televised live. I was riveted for 2 hours, and today I have spent most of the morning watching CNN rather than SportsCenter or basketball. Rather than just post something glib on sports or try to be overly emotional which would probably end up overly saccharine or seem disingenuous, I also didn’t want to gloss over this enormous tragedy, so I have decided to re-post Anthony’s post at V-W from this morning, as it is both scientific and informative, something that is both unusual for this site and befitting my personality a little bit better.
Yes, this is a weather blog, and earthquakes and tsunamis are in no way, shape, or form are affect by meteorological forces, but when a natural disaster of this magnitude occurs and affects this many people, it’s impossible not to discuss it from a scientific standpoint. It was a rather surreal scene last night, after randomly noticing that ALL of the trending topics on Twitter had a Japan reference, switching on CNN and watching live aerial footage of the tsunami rushing inland and taking out houses, roads, villages, farmland, and just not stopping as it plunged inland. Clearly this will remind people of the giant 2004 Sumatra Earthquake/tsunami and the devastation it caused, but this was different in a way that we could see everything unfold live on TV, whereas back in 2004 we heard about nearly everything a bit after the fact.
What exactly causes a tsunami of this magnitude? Well on Wednesday a 7.2 earthquake hit off the Japanese coastline, followed by a 6.3 early Thursday, then on Friday afternoon, the monster 8.9 quake hit about 230mi northeast of Tokyo, or due east of Sendai. The main instigator of the tsunami was that it only happened at 15.2mi below the surface, which is very shallow for such a powerful quake, and means most of that energy is translated to the surface. Unlike the Sumatra quake, in which a massive underwater landslide triggered the tsunami, this quake caused an uplifting of the seafloor in the Japan Trench as the Pacific Plate subducts underneath the Eurasian Plate, pushing it upwards. When the seafloor has a sudden lift, all of the water above it is displaced, and when you have THAT MUCH water moving upwards, it has nowhere to go but outwards. Out in the open sea, you wouldn’t really notice much as the amplitude (height) of the wave might only be a foot, but the wavelength (distance between wave crests) can be dozens or even hundreds of miles long. When this wave approaches the shallow waters near a coastline, the energy of the wave causes it to rapidly build in height and then just inundate the coastline. When you see a normal wave on a coastline, the water will only go inland a few feet before pushing back out to sea in anticipation of the next wave just a few seconds later. With a tsunami wave, and the fact that the waves are dozens of miles apart, all of that energy pushes the wave inland hundreds of feet, or even a couple of miles depending on the topography, past the coastline before it starts to recede ahead of the next wave.
Tsunami waves can reach upwards of 500-600mph as they race across the open ocean, as evidenced by the waves reaching Hawaii and reaching heights of 7 feet, flooding up to 100ft of coastline according to some early reports. Currently, these waves are currently making their way to the Western US. Granted the West Coast won’t see anything like what our friends in Japan unfortunately experienced, but still not a wise time to be standing on the beach. Our thoughts and prayers go out to Japan and all of the people affected by this disaster, and hope our readers who have friends or family traveling abroad hear good news.