The Zaō Mountains (蔵王連峰, Zaō Renpō), commonly called Mount Zaō, are a complex cluster of stratovolcanoes on the border between Yamagata Prefecture and Miyagi Prefecture in Japan. The central volcano (one of the 100 Famous Japanese Mountains) includes several lava domes and a tuff cone, Goshiki-dake, which contains a crater lake named "Okama". Also known as the "Five Color Pond" (五色沼, goshiki numa) because it changes color depending on the weather, it lies in a crater formed by a volcanic eruption in the 1720s. The lake is 360 metres (1,200 ft) in diameter and 60 m (200 ft) deep, and is one of the main tourist attractions in the area.
One striking feature of Zaō's famous ski resorts are the "frost-covered trees" (樹氷, juhyō) that appear in mid-winter. Strong wind over the nearby lake fling water droplets which freeze against the trees and their branches, until near-horizontal icicles begin to form. Falling snow settles on the ice formations, with the end result being grotesque figure of a tree. The effect of a full forest of such trees gives visitors a ghostly impression, hence they are colloquially known as "snow monsters". Formed under precise precise meteorological and ecological conditions almost unique to northern Japan, the phenomenon is has been decreasing due to climate change.
