Gaua (formerly known as Santa Maria Island) is the largest of the Banks Islands in Torba Province of northern Vanuatu. It covers 342 km².
It has rugged terrain, reaching up to Mount Gharat (797 m), the peak of the active stratovolcano at the center of the island. The most recent eruption was in 2011. The volcano has a 6 x 9 km caldera, within which lies a crater lake known as Lake Letas, the largest lake in Vanuatu. To the east of the lake is Siri Waterfall (120 m drop).
The island has a population of 2491 (in 2009), with an annual growth rate of 2.0 percent. This population is scattered in various coastal villages on the western, southern and northeastern sides of the island. The eastern side has a few hamlets with an immigrant population coming mainly from the two smaller islands Merig and Merelava, southeast of Gaua. The largest village is Jolap, on the west coast.