Aðaldalur, (“Main valley”) a broad lowland area at the head of Skjálf­anda­flói gulf, between the river Skjálfandafljót and Hvammsheiði moor, and then east of Fljótsheiði moor to the lake Vestmannsvatn. It lies largely on the Aðaldalshraun lava field, which comes from the Lake Mývatn area. Widespread birch bushes and strangely beautiful lava formations. Farms along the edge of the lava. Belts of sand along the coast.