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Recent analysis of satellite data shows that the Japan Alps are sinking up to 5 mm per year, according to government geographers.

It is unclear whether the sinking has been happening over a short time or caused by crustal changes, the researchers at the Land, Infrastructure and Transport Ministry’s Geographical Survey Institute said.

Theoretically, the mountain range should be rising because it is being squeezed by crustal movements from both the east and west, they said.

According to one of the geographers, Makoto Murakami, this is the first time researchers have detected that the Alps are sinking. Usually, mountains rise or sink due to changes in the Earth’s crust, such as plate movement.

The findings are part of a study on the changes in geographical heights at various locations nationwide. The institute uses the global positioning system to observe changes in crustal movements at about 1,200 sites.

The study used the data on the Alps and other areas collected from 1996 to 2002, Murakami said.

In the past, heights were measured along main roads. But this method cannot detect sinking because it is impossible to measure the entire area of mountain ranges, the researcher said.

The Japan Alps straddle Nagano, Niigata, Toyama, Gifu, Yamanashi and Shizuoka prefectures in central and eastern Japan.

While the GPS data showed that other parts of Japan are sinking or rising, these movements can be explained by plate movements or extraction of groundwater, and there are no contradictions with data obtained through previous measuring methods, according to the researchers. Only the data on the Japan Alps are inexplicable.

“Because the measuring points for the GPS system are located at the base of mountains or on mountainsides, we cannot tell if the summits are sinking,” Murakami said. “We would like to collect more data and further analyze movements beneath the Earth’s crust.”