Lava Pillow Lava 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. Photograph by Jack Lockwood, U.S. Geological Survey, June 14, 1982.
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. The round cobbles were transported by the river.