Mysterious finds, which confused geologists for two hundred years, turned out to be traces and harbingers of strong earthquakes. Scientists realized that strange cones in the ground appeared in the place of asteroid falls or indicate places with increased seismic activity. The strange finds, which have remained a mystery to archaeologists for almost two hundred years, turned out to be intricate messages from the distant past of the Earth, which remained at the site of powerful earthquakes. This conclusion was made by scientists from the University of Applied Sciences Neu-Ulm (Germany).
With their characteristic bulging head and tapering tails, these sand spikes are somewhat mushroom-like.
However, the reason for these unusual geological bodies in the earth has remained a mystery since their first discovery in the 20s of the 19th century. According to various versions, these cones are stalactites, fossilized by ancient algae, turnips or mushrooms, fulgurites (pipes sintered when struck by lightning), burrows of ancient animals filled with sand, etc.
“I would call them geological curiosities,” says Lydia Lonergan, a geologist at Imperial College London. "They are quite unusual."
For the first time, sand cones were found almost 200 years ago in southern Germany near the Nördlinger Rice meteorite crater. Half a century ago, it was believed that a crater with a diameter of 24 km is of a volcanic nature, but today it is known that it was formed when a kilometer meteorite fell to the Earth about 14.8 million years ago. In 2010, scientists proved that the impact of this meteorite caused an earthquake with a magnitude of 8.5.
Over the past three decades, geologist Elmar Büchner and colleagues have collected thousands of different sand cones in the vicinity of the basin. These solid geological bodies, the largest of which are more than a meter in length, are found only in those sedimentary rocks that date back to the time of the meteorite's fall. But the main thing that the scientists paid attention to was the nature of their location.
“Thick heads of sandy spikes indicate a seismic source,” Buechner explained.
At first this circumstance seemed unexpected to geologists, but soon they remembered the orientation of the cones found thousands of kilometers away - in the Imperial Valley in southern California. Over 95% of similar cones found there face east towards the San Andreas Fault between the Pacific and North American plates along the US coast. Thus, scientists have found that earthquakes play an important role in the formation of these strange bodies. Moreover, the presence of these cones not only speaks of the past earthquake, but also indicates the direction to the source of the tremors.
In a recent paper published in the journal Nature Communications, Buechner suggested the mechanism by which these cones are formed. Their formation requires a powerful earthquake, loose sand, water and calcite, which acts as an adhesive. The process begins with the passage of the fastest, so-called P - waves (primary waves or pressure waves), which compress the sand and squeeze out all or almost all of the moisture from it. “The sediment is almost completely dry, but some water traps remain there,” explained Buchner.
A few seconds later, slower, secondary S-waves pass through the sand. The passage of these waves causes the remaining water traps to heat up and instantly vaporize in an explosive manner. As a result of each such explosion, a hollow structure remains in the sandstone, the tapering tail of which is directed away from the source of pressure.
The surrounding sand then quickly fills the resulting cavity, and calcite, which is the main mineral in the sandstone composition, holds the new structure together.
The whole process, according to scientists, takes a few seconds. “Most of our rocks are formed at least millions to tens of millions of years. The process takes place in the blink of an eye, ”said Franek Hasyuk, a geologist at the Kansas Geological Survey who was not involved in the study.
In addition to Germany and California, unusual cones are found in only a few places on Earth - for example, in Italy, France and Australia. Taking this into account, it should be assumed that they are formed during really powerful earthquakes - with a magnitude above 7-8, says Buchner.
For this reason, sand cones can serve as markers for especially powerful, destructive earthquakes, and therefore it is not worth building nuclear power plants and schools where these formations have already been found, Khasyuk said. “Understanding ancient seismicity can really help us plan our infrastructure more meaningfully,” he says.
bbabo.Net