Fair Weather Event Buttercup — But What’s That Rumbling?


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Chile this weekend

In Chile this weekend, there are a few clouds in the Andes, but the coast is clear. Satellite photo courtesy of NASA.

Modern mass media concentrates on the bad — bad weather, bad economies, bad guys in hoods. Once in a while it’s comforting to realize that there are some good things in the world — even the weather world. So Decoded Science is highlighting fair weather this Friday, and naming the event after a flower.

This week’s Fair Weather Event is called Buttercup. Since the weather in the northern hemisphere is having its winter tantrum, we’re headed down to 40 degrees south latitude — to Valdivia, Chile.

The Climate Of Valdivia, Chile

Valdivia is at about the same latitude as New York, and each is on a large ocean. But there’s a huge difference in the climates.

New York faces east and its weather comes mainly from the continent. Valdivia faces west and has an oceanic climate. If you’re looking for a place in the middle latitudes where the temperature doesn’t vary much with the seasons, Valdivia fits the bill: daytime temperatures around 70 in summer and 50 in winter. Compare that with New York, which swelters in the summer and freezes in the winter — especially right now.

This weekend, Fair Weather Event Buttercup will feature Valdivia at its best. An easing of the maritime flow will allow daytime temperatures to reach 80 degrees, a fairly unusual occurrence.

Normally winds blow off the Pacific Ocean. Nearby waters are now at their maximum temperature for the year — about 60 degrees, warm enough for a swim if you’re hardy. In the winter, the water temperature bottoms out at 50 degrees and keeps the winters relatively mild.

The Chilean Chinook: Puelche

A chinook, or foehn, wind, blows down a mountain and is heated as the pressure increases upon descent. The Santa Ana of southern California is a well-known chinook that can raise temperatures to 100 degrees in Los Angeles.

Puelche, named for an indigenous tribe, is a modest foehn, but it will be responsible for this weekend’s temperatures of about ten degrees above average.

Normally high pressure stays offshore. But occasionally it stretches inland north of Valdivia, bringing easterly winds (the wind blows clockwise around high pressure in the southern hemisphere). Puelche winds are dry, as the moisture has been precipitated out in the mountains.

Precipitation In Valdivia, Chile

Valdivia is a rainy place — but not now. Valdivia averages over 70 inches of rain per year, nearly twice that of New York and more than any US city. But the rain falls mainly in the winter. This weekend will be rain-free — in fact, it will be cloud-free.

So maybe you’re thinking of moving to Valdivia. There’s something you should know about the place: It has a fault. Actually, it sits on a fault. Decoded Science’s Geoscientist Jennifer Young shares her insight on this topic here:

Jennifer Young, Geoscientist, tells us that it's all Chile's fault...

Jennifer Young, Geoscientist, tells us that it’s all Chile’s fault…

The Biggest Earthquake Ever? Valdivia, 1960

Chile has the doubtful distinction of being the location of the Earth’s largest recorded earthquake — a magnitude M9.5 (or M9.6; estimates vary and the USGS, in different places, cites both) in 1960. It’s not impossible that this particular ‘Big One’ was the largest ever, because although the earthquake scale is theoretically open-ended, maximum magnitude is determined by the strength of rock and the 1960 event is right up there at the top of the scale.

The tremor resulted from the collision of the Nazca plate with the continent of South America. The former, being cold, dense oceanic crust, is descending beneath the warmer, more buoyant continental crust of the latter; in such settings, a build up of friction is released as an earthquake.

Other Earthquakes Were More Damaging

Given its size, the 1960 tremor did relatively little damage compared to others such as the Boxing Day earthquake and tsunami of 2004, the Japan earthquake of 2010 and even a much smaller (M7.8) tremor, also in Chile, which killed an estimated 20,000 people.

Valdivia, Chile after the 1960 earthquake

Valdivia, Chile after the 1960 earthquake. Photo courtesy of NOAA

Nevertheless, the statistics for the 1960 event are bare and brutal. The USGS sums up the damage: “Approximately 1,655 killed, 3,000 injured, 2,000,000 homeless, and $550 million damage in southern Chile; tsunami caused 61 deaths, $75 million damage in Hawaii; 138 deaths and $50 million damage in Japan; 32 dead and missing in the Philippines; and $500,000 damage to the west coast of the United States.”

Will It Happen Again?

Almost certainly, although possibly not on quite such a large scale, at least for some time. Citing various historical sources and geological studies as far back as 1575, seismologist Robert Yeats quotes a recurrence interval of 128 years for large earthquakes off southern Chile, though without defining ‘large’ (the magnitude of earthquakes prior to the development of the seismometer in around 1900 is uncertain).

This matters, because a large earthquake in an offshore subduction setting, especially if it triggers a significant tsunami, can be very damaging indeed; and the deadliest in Chile was the 1939 tremor mentioned above at just M7.8.

A quick look at the USGS earthquake database shows that Chile has experienced 11 earthquakes of at least M8.0 since 1900 — an average recurrence time of less than 11 years. Three have occurred in the last five years; the most recent was in 2014. But the 1960 event is the daddy of them all — releasing more than 11 times as much energy as the next largest on record along the Peru-Chile Trench.

Back to you, Jon… 

What To Expect If You Visit Valdivia This Weekend

Will there be an earthquake? Let’s do the math.

There have been 11 earthquakes of M8.0 or greater in the region in the last 114 years, nearly 42,000 days. So if you go for two days, the chances of having a major earthquake is about one in about 21,000. Even given the increasing frequency of major earthquakes in recent years and the fact that a smaller earthquake could be damaging, it’s still not worth buying earthquake insurance.

And the weather will be perfect.

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