St. Vincent is a rugged island of volcanic formation, and the Grenadines are formed by a volcanic ridge running north–south between St. Vincent and Grenada. The highest peak on St. Vincent is Soufrière, an active volcano with an altitude of 1,234 m (4,048 ft); it has a crater lake 1.6 km (1 mi) wide. In the center of the island, Richmond Peak rises to a height of 1,079 m (3,539 ft). Only 5% of the island's surface has slopes of less than 5°. The low-lying Grenadines have wide beaches and shallow bays and harbors, but most have no source of freshwater except rainfall. The highest point in the Grenadines is Mt. Tobai on Union Island, with an altitude of 308 m (1,010 ft).