Hagi Geopark: Kasayama Area
Mt. Kasayama (112 m) is Hagi’s youngest volcano. Its name, which literally means “sedge hat mountain,” comes from the mountain’s resemblance to a type of wide-brimmed sedge hat called an ichimegasa. Around 11,000 years ago, a huge eruption spread lava across the area, creating a plateau. Some 2,200 years later, an eruption of pyroclastic fragments created a conical mound of scoria with a crater at the summit, and 7,000 years ago, sea levels rose, turning the mound into an island. The motion of the waves gradually created a sandbar that reconnected the mound (that would later be known as Mt. Kasayama) to the mainland.
Mt. Kasayama is a part of the Abu Volcano Group, which is made up of 50 volcanoes in the general vicinity of Hagi. The flat-topped islands visible across the bay are the tips of underwater volcanoes in the same group. The Abu volcanoes are unusual, however, in that each volcano was formed by only one eruption.
It is possible to walk from the Mt. Kasayama Observatory site at the summit down into the crater. At the southern base of Mt. Kasayama is Myōjinike Pond. Myōjinike is a saltwater pond, and local fishermen sometimes release fish there as an offering to the nearby shrine. In the woodland behind the shrine are kazaana, or “wind holes,” fissures in the rock-strewn forest floor out of which cool air blows. During the winter, denser cold air settles deep into the fissures, and, as the weather warms, the cool air expands and blows out of the fissure, cooling the area around it. Even in midsummer, the temperature remains a moderate 15 degrees Celsius.
Access: 40-minute walk from Koshigahama Bus Stop, 20 minutes by Bōchō bus from JR Higashi Hagi station or Hagi Bus Center. 20 minutes by taxi from the Hagi Bus Center.
Google Maps link: here