The foreset beds are part of a lava delta that grows towards the ocean and provides a platform on which subaerial lavas can extend, thus adding new land to the island. However, some lobes are not continuous and break apart to form pillow sacks, thus adding rubble to the flank of the volcano. The active front of a lava delta is called a bench. Like the delta, the bench is built on rubble. A visitor, standing on the bench at the time of the collapse, disappeared into the ocean.
Dark areas are black sand.
Photograph by Christina Heliker, U.S. Geological Survey, August 25, 1994. Pillow lavas are also found near the summit of Mauna Kea These pillow lavas were produced by a subglacial eruption that occurred 10,000 years ago. Figure 21.11 from Porter, 1987. Pillow lavas can also form when flows enter a river or lake. The pillows in the photo formed in the Wailuku River above Hilo, Hawaii about 3,500 years ago.