JP-649527 The crater of Mount Aso ( 阿蘇山 )

Mount Aso ( 阿蘇山 ) is the largest active volcano in Japan and is among the largest in the world. It stands in Aso Kujū National Park on the island of Kyushu. Its peak is 1592 m above sea level. Mount Aso has one of the largest calderas in the world (25 km north-south and 18 km east-west). The caldera has a circumference of around 120 km (75 mi).

[ Note: A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption.]

This postcard from Yoko (Postcrossing) shows the crater of Mount Aso.