Browns Island, or Motukorea, is one of the best preserved volcanoes in the Auckland Volcanic Field. Located north of Musick Point, it erupted some 8,000 to 12,000 years ago, exhibiting a range of volcanic activity including ash, lava and scoria eruptions. Due to centuries of cultivation, little native bush remains except on the north-eastern cliffs, leaving the volcanic landforms easily visible. The island consists of several scoria cones, a small remnant of a tuff crater, and the higher portions of the lava flows. The area was dry land when the eruptions occurred, but much of the lava is now submerged at high tide.
There are three pa sites on the island, with the largest occupying the slopes of the main scoria cone. The island's highest point is 68 metres above sea level.
Browns Island is part of the Hauraki Gulf Maritime Park. It is not served by ferries, so private boats are the main means of access.
A mineral found here, motukoreaite, has been named after the island.
