Chile has a long history of tsunamis, so when a magnitude 9 earthquake struck far-away Japan on March 11, 2011, residents of this beautiful country that stretches along the Pacific coast of South America were quick to evacuate low-lying areas. Fortunately, that tsunami’s energy weakened during the 22 hours it took to cross the Pacific. By the time it reached Valparaiso, according to NOAA’s National Geophysical Data Center, the waves, at a maximum height of 1.54 meters, or a little over 5 feet, caused only mild damage.
However, Chileans have not always been so lucky.
♦ The biggest earthquake in the world
According to the University of Washington, earthquakes underneath the ocean generate tsunamis by suddenly deforming the sea floor and displacing the overlying water, sending it rippling outward in all directions. These ripples, although only some 3 feet high (1 m) out on the open sea, have a long wavelength (often more than 60 miles, or 100 km, in between waves), and physics dictates that they will travel very quickly through deep water, speeding along at well over 400 mph (700 km/h). When each wave reaches shallow water near shore, friction with the seabed slows it down somewhat, but this also causes the wave front to rise to as much as 30 feet high (10 m) or more.
Both this terrible speed and the high, foamy wave front can be seen in videos of the incoming tsunami caused by biggest earthquake of modern times, a magnitude 9.5 shallow quake that struck near Valdivia, Chile in May 1960. See, for example, the images starting at 5:12 in this Spanish-language public service video from the Seismology Center of the University of Tarapacá, Chile.
It was only one of the 112 tsunami events that the National Geophysical Data Center reports for Chile since record-keeping began in 1562, but the massive Valdivia earthquake happened so close to the country’s coast that the first tsunami effects started only 10-15 minutes after the shaking ended. This gave survivors little time to recover and react.
The biggest wave was 82 feet (25 m) high, and according to the USGS, “Most of the casualties and much of the damage was because of large tsunamis which caused damage along the coast of Chile from Lebu to Puerto Aisen and in many areas of the Pacific Ocean. Puerto Saavedra was completely destroyed by waves which reached heights of 11.5 m (38 ft) and carried remains of houses inland as much as 3 km (2 mi). Wave heights of 8 m (26 ft) caused much damage at Corral.”
♦ Chilean tsunamis
Not all earthquakes cause tsunamis, only those with an intensity greater than or equal to about magnitude 7 on the Richter scale. These should be fairly close to the surface, with epicenters in the upper 30 miles (50 km) of the Earth’s crust, and of course, they usually happen beneath the sea.
Unfortunately for Chile, it sits in an ideal location for such events, right on the infamous “Ring of Fire.” Just offshore, the edge of the Nazca tectonic plate is subducting underneath the plate that carries the South American continent. This causes many large quakes, including the so-called “megathrust” events, like the Valdivia earthquake in 1960, which are the most powerful known on Earth.
Chile’s most recent big tsunami happened on February 27, 2010, when a shallow magnitude 8.8 earthquake, centered offshore at a location about halfway between Valdivia and Valparaiso, caused a tsunami with a maximum wave height of some 95 feet (29 m). This earthquake, named after the Bio-Bio region of Maule, Chile, where it occurred, inflicted an estimated $30 billion economic loss on the country and was the sixth most powerful earthquake instruments have ever recorded anywhere in the world.
With all this activity in southern and central Chile, it comes as something of a surprise to non-Chileans that geologists who have tracked down the oldest known tsunami in Chile (around 1.8 million years ago) say that the northern Chile coastline (along with part of southern Peru) has the highest potential in all South America for earthquakes and tsunamis. Local residents, however, agree. They remember the massive earthquakes and tsunamis in the second half of the 19th century that destroyed the city of Arica and caused extensive damage throughout the region and around the Pacific.
Chile sometimes generates Pacific-wide tsunamis, but it is also vulnerable to tsunamis from other earthquake centers around the Ring of Fire. Such tsunamis, though, usually have a much smaller wave height since they have a longer way to travel. For instance the highest measured tsunami in Chile from the second biggest earthquake in modern times – the magnitude 9.2 Alaska earthquake of 1964 – was 13 feet (4 m) in Coquimbo, still enough to do some damage, but thanks to the long lead time, it caused no injuries or fatalities.
Chile has experienced one or more tsunamis from magnitude 8 or stronger local earthquakes every century for the last 450 years. So far in the 21st century, though, its largest tsunamis have come from a distance (Japan in March 2011 and New Zealand in July 2011). These waves have all been fairly small so far.
However, Chileans are prepared, for they have learned from history. In Chile, it’s only a matter of time before the ground will shake again and the waters will recede from the coast, only to pile up and come racing in again as a huge tsunami.
