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in one study Published last month in Nature Communications, Dr. Buchner and his collaborators have proposed a recipe for how sand spikes form. Among the essential components the researchers suggest are strong ground shaking, loose sand, water, and calcite, which acts as a glue.
The researchers suggest that the process begins when the fastest-moving seismic waves, or primary waves, travel through the sand and compress it. Dr. This sends most, but not all, of the moisture in it to the surface, Buchner said. “The sediments are basically dry but there are still a few pockets of water.”
After a few seconds, slower seismic waves, called secondary waves, ripple through the sand again. These waves trigger dramatic increases in pressure that cause the remaining water reservoirs to rapidly heat up and then explosively evaporate. Each explosion reveals a hollow structure that creates a tail that faces away from the pressure source. The surrounding sand quickly flows back into the cavity and bonds the calcite structure, the primary mineral in limestone.
The researchers suggest that the sand spikes likely formed within a matter of seconds. Franek Hasiuk, a geologist with the Kansas Geological Survey, who was not involved in the study, said it’s different from most other geological structures. “Most of our rocks take at least millions to tens of millions of years to form. That happens in the blink of an eye.”
Aside from Germany and California, sand spikes have been detected in only a few places. Dr. Buchner and colleagues suggest that particularly strong ground shaking must have been necessary to create them, given their relative scarcity.
Dr. Because the sand spikes are signs of intense, potentially devastating ground shaking, they are valuable indicators of dangerous conditions, Hasiuk said. “It would be a bad idea to build a school or nuclear power plant where the dunes are,” he said.
“Understanding legacy seismicity can really help us plan our infrastructure more intelligently.”
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