Monday, November 11, 2013

Today in Lighthouse History

November 11, 1921—The keepers of Los Angeles Harbor Lighthouse at the tip of the San Pedro Breakwater filed the following report with the Superintendent of Lighthouses, San Francisco:

I respectfully report a most unusual submarine disturbance in the vicinity of this station yesterday. It began at 10 a.m. and continued to recur at regular intervals through the afternoon and evening. The water of the bay would become violently agitated and swirl around in a whirlpool for about ten minutes, then suddenly slacken and run backwards slowly. At times there would be a 7 to 8 knot current flowing underneath the lighthouse wharf. The steam Daisy Matthews, inbound and lumber-laden, was seen to careen and be thrown off her course and driven rapidly eastward when she poked her bow around the breakwater. The battleship Arizona, anchored at her berth 300 yards north of the station, make 8 or 10 complete cycles during the afternoon and dragged anchor slightly. On her last turn, at 4 p.m., her stern was within 75 feet of the rocks at the base of the tower. She was then removed to an anchorage near Long Beach. A shore boat came alongside the wharf and reported that the tide was running like a millrace under the drawbridge in the Inner Harbor, and there was an 8 knot current at Deadman’s Island. The earthquake theory has been suggested as accounting for this phenomenon.

Elinor's Note: The report was probably correct about the earthquake. The Journal of Geophysical Research for December 1922 carried an abstract for an article about the November 2011 earthquake in Australia that probably caused the phenomenon at Los Angels Harbor Lighthouse:

There was a record of an earthquake on the magnetograms of the Watheroo Magnetic Observatory, Western Australia, on November 11, 1921. The declination and horizontal-intensity traces showed a slight broadening, while there was a very slight blurring of the vertical-intensity trace. The extreme Greenwich mean times of the record were from 18h 45m to 19h 0lm for declination, 18h 44m to 18h 56m for horizontal intensity, and 18h 52m to 18h 59m (uncertain) for vertical intensity. Mr. Curlewis, Government Astronomer at Perth, reported the following times of phases as obtained on the seismograph: 18h 43m 56s.6, P; 18h 46m 00s.5, uncertain; 18h 50m 10s.4, L.

Earthquakes near or at sea create seismic energy waves that can travel long distances and cause tidal and wave fluctuations as they shoal up in harbors and their waves come on shore. These earthquake tsunamis can be huge, as we know from the tsunami in Japan several years ago. Today's Pacific Tsunami Warning System (established in 1946) warns of these events.

Los Angeles Harbor Lighthouse, nicknamed Angel's Gate Light, was built in 1913. It takes its share of pummeling from tremors and earthquakes and from storms and wind too. One storm caused the concrete platform on which it sits to sink on one side, giving the tower a slight list. The same storm slammed the tower with a wind gust that knocked one of the lightkeepers to the floor.  The lighthouse was destaffed in 1971 and now operates automatically. It guards one of the largest shipping ports in the world at Long Beach. (Images courtesy of the U.S. Coast Guard.)


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