Monday, October 5, 2009
The Samoan Tsunami goes local
Its interesting that coverage of the Samoan Tsunami of September 29th has largely been overshadowed by the Indonesian earthquake, which resulted in greater loss of life. Surprisingly, though, the Samoan tsunami did show up on the west coast and, for that reason, was of particular interest to me. Thankfully, it didn't show up in a BIG way.
When the tsunami struck Samoa I was working in San Diego and found myself extremely intrigued by the tsunami warning that was released for the west coast. It is no surprise that waves generate and travel over entire ocean basins, but I found this one particularly exciting, if only because I was in an ideal position to watch it propagate around the globe, and am now surrounded by people at USGS who get REALLY into these things.
At about 8:30 pm on the 29th I went to NOAA's Tides and Currents site (http://tidesandcurrents.noaa.gov) and pulled up real-time water level data for San Diego, Monterey and Port Angeles. By about 9:00 pm the waves were visible in the data stream in San Diego, showing up as waves with an amplitude of about 1/2 a foot and a wavelength of about 30 minutes. The same wave signature showed up shortly after in Monterey, CA and just after midnight in Port Angeles.
USGS scientists Andy Ritchie (who, as an aside, is from Port Angeles) was in Santa Cruz on the bridge over the harbor and reported: "at around 9:26 the first (negative) wave appeared. The water surface dropped by about 50 cm over a period of five minutes or so, then rose about 1.4 m from the low over about the next 7.5 minutes. I watched this through another two waves, when the amplitude began to decrease somewhat. It looked like maximum water velocities were somewhere around 4 m/s - which was pretty impressive to me. Other than some surprised-looking gulls and slightly distraught pelicans zipping back and forth on the current, and some impressive turbidity getting kicked up, it seemed like everything stayed put. There were some curious (brave? foolish?) folks in a rowboat that rowed out of sight before the tsunami came, and I imagine they felt a bit like the seagulls and the pelicans."
I was particularly delighted to find the signature of the tsunami in NOAA's water level data from Port Angeles, which you can see here. I can't help but wonder if these relatively small events have any impact whatsoever on geomorphology or coastal habitats on the west coast.