Several weeks ago, an offshore earthquake caused a tsunami warning to be issued for the California coast. It was soon cancelled, but the incident was a reminder of the danger earthquake-induced tsunamis pose.
Louisiana has never experienced a tsunami because it does not lie in an area where tectonic plates collide. We do occasionally experience small earthquakes along minor fault lines, but none are powerful enough to cause a tidal wave.
However, on March 27, 1964, tsunami-like waves did unexpectedly strike the Louisiana coast and cause minor damage. Incredibly, they were the result of an earthquake that occurred 3,600 miles away.
On that Good Friday, a 9.2 magnitude earthquake rocked Alaska. The Good Friday Earthquake was the strongest ever recorded in North America and the second strongest recorded anywhere (the record was set by a 9.5 magnitude quake that shook Chile in 1960).
The temblor caused the land to rise thirty feet in some areas and drop eight feet in others, and Anchorage, Valdez and other towns were severely damaged. Collapsed structures and tsunamis that swept as far as Washington and Oregon killed 131 people.
On March 27, 1964, tsunami-like waves did unexpectedly strike the Louisiana coast and cause minor damage. Incredibly, they were the result of an earthquake that occurred 3,600 miles away.
The earthquake also created a shockwave that raced deep underground and reached Louisiana in just twelve minutes. Then, for half an hour, a series of waves measuring three to six feet high rushed eighty miles up rivers, bayous and canals along four hundred miles of the Louisiana-Texas Gulf coast. Boats were hurled around as mooring lines snapped and debris crashed into docks. Fortunately, no major injuries were reported, but there was minor damage in Grand Isle, Galliano and Des Allemands.
Most newspapers referred to the waves as tidal waves, but as the Lovington (New Mexico) Daily Leader explained, that really wasn’t the case. A tidal wave, or tsunami, is caused by a strong offshore earthquake that forces a wall of water into the coast. The geologic structure around Louisiana does not create those types of earthquakes.
Instead, the Good Friday quake was so powerful that it rippled the earth’s surface. Incredibly, the city of Houston, Texas, was lifted up nearly four inches when the shockwave passed beneath it.
Rev. Louis J. Eisle, director of the seismographic observatory at Spring Hill College in Mobile, explained what happened to the newspaper. “The Louisiana coast is delta land and is very, very deep with Mississippi River sediment, which is quite flexible like jello. The large amplitude motion in the earth along the Gulf Coast caused this plastic sediment to quiver, again like jello.”
There were numerous reports of unusual water activity. One Baton Rouge couple reported the water in their swimming pool suddenly started “going wild.” And a Denham Springs resident who saw a wave of water rush up the Amite River declared, “I never heard water roar like that on Amite River before.”
This “quiver” caused the water lying above the sediment floor to slosh around violently. Surprisingly, it didn’t take much ground displacement to create the unusual waves. Seismographic instruments showed one-quarter of an inch displacement in Mobile and just one-sixteenth of an inch along other parts of the Gulf Coast.
There were numerous reports of unusual water activity. One Baton Rouge couple reported the water in their swimming pool suddenly started “going wild.” And a Denham Springs resident who saw a wave of water rush up the Amite River declared, “I never heard water roar like that on Amite River before.” According to the Associated Press, the bottom of the five-foot-deep Amite River was briefly exposed when the water rushed back out.
In Golden Meadow and Cut Off water from Bayou Lafourche spilled over the highway and left logs and other debris in the road. One wave at Golden Meadow even washed into a bar and forced the customers to flee.
A New Orleans nightwatchman reported that the water in the Industrial Canal rose six feet almost instantly, and offshore oil workers watched as the Gulf below their rigs suddenly dropped five feet below normal and then shot up five feet above normal.
The dramatic water displacement occurred as far west as Houston. The Monroe Morning World reported a Houston Pilots Association spokesman as saying, “It was weird. The water was rolling and bubbling up throughout the ship channel as if something was underneath it.”
Geographer Dr. Sherwood M. Gagliano investigated the various reports and concluded that the shockwave had triggered land movement along some of Louisiana’s fault lines. It was movement along these faults that caused cracks in a Baton Rouge city swimming pool and the collapse of a concrete wall at a New Orleans water treatment plant.
According to Dr. Gagliano, the Good Friday Earthquake and its far-reaching shockwave increased fault line movement in Louisiana for more than a decade afterwards and accelerated coastal erosion because of the subsequent land subsidence.
Dr. Terry L. Jones is a professor emeritus of history at the University of Louisiana at Monroe. For an autographed copy of “Louisiana Pastimes,” a collection of the author’s stories, send $25 to Terry L. Jones, P.O Box 1581, West Monroe, LA 71294.
