Geology
Okinawa archipelago
Okinawa is an island of tectonic origin, 107 km long and 31 km wide. The southern part of the island (approximately one-third of its area) is a lowland built up with cities and American air bases. The northern part of Okinawa (two-thirds of the island) is a highland, represented by hills, low mountains, and rocks. The northern part is forested, with isolated villages found mostly on the coastline.
The island's river system is very poor, as there are practically no rivers. A small number of artificial canals are located in the seaport areas.
The lakes are small and their number is also insufficient for full water supply. The largest of them are Lakes Fukugami, Kanna, and Kuina. They are located in the northern forested part of the island.
Lakes of Okinawa
Fukugami, Kanna, Kuina
But why don't Okinawans worry about the annual drought? Because, from June to September (although every year is different), the typhoon season begins, which is also called the "fifth season of Okinawa."
Typhoons are tropical cyclones in the Northwest Pacific Ocean. In fact, it is a strong wind whirlwind (25 m/sec and faster) that forms in the ocean and is accompanied by constant incredible rains, storms, floods, etc.
It is typhoons that fill reservoirs.
Despite their benefits, typhoons are a natural disaster. Heavy rains cause floods, strong winds break trees, destroy old buildings and communications, overturn cars and destroy plantations.
One typhoon lasts about a week, and there can be 3-5 during the typhoon season.
The air temperature at this time does not decrease, the humidity is one hundred percent, so a suffocating greenhouse effect is formed.
The caves
Due to the high content of limestone deposits in Okinawan rocks, many caves have been formed. The largest of them are in Tamagusuku city, in the south of the island, and in Uruma city. The cave in Tamagusuku, Gyokusendo, is approximately 5 km long, 850 meters of which are open to the public. The cave has many fresh and salt water bodies. Scientists estimate the age of Gokusendo cave at three hundred thousand years. Stalactites and stalagmites grow here at a rate of 1 millimeter every three years, much faster than in other prefectures. It is said that the secret of their speed is the subtropical climate of Okinawa.
The cave in Tamagusuku city is considered the most beautiful in East Asia.
Earthquakes
On Okinawa and its neighboring islands, one type of mountain folding can be traced - capricious rocks and hills, randomly scattered and usually low in height (up to 200 meters).
Their formation was caused by constant seismic fluctuations: from a few hundredths to six to seven points.
Most often, the magnitude of earthquakes in Okinawa is 3-4.
The constant earthquakes on the territory of the Ryukyu archipelago are due to the fact that the island is located in a subduction zone, i.e. on a part of the lithospheric plate that sinks under another lithospheric plate in the fault area. In our case, the Philippine plate, on which Okinawa is located, is simultaneously submerged under two other plates, the Eurasian and Amur plates.
Okinawian beaches
As I mentioned above, Okinawa has many limestone deposits. These deposits form rocky spurs on the coast. Over time, due to the accumulation of sedimentary rocks and rising ocean levels, some rocks collapse and/or disappear underwater, forming limestone reefs.
Okinawan beaches are among the most beautiful in East Asia and are popular among Japanese from central Japan. In the Japanese mind, "going to Okinawa to relax on the beach" is a very expensive vacation.