two periods of volcanic evolution were extremely brief, something first noted in 1988. The forest-covered summit of the volcano consists of many cones which generated lava from its two rift zones between 240,000 and 120,000 years ago. Kohala completed its shield-building stage 245,000 years ago and has been in decline ever since. Potassium-argon dating indicates that the volcano last erupted about 120,000 years ago in the late Pleistocene. Kohala is currently in transition between the postshield and erosional Hawaiian volcanic stages in the life cycle of Hawaiian volcanoes. The United States Geological Survey has assessed the extinct Kohala as a low-risk area. The volcano is in zone 9 (bottom risk), while the border of the volcano with Mauna Kea is zone 8 (second lowest), as Mauna Kea has not produced lava flows for 4,500 years. Kohala, like other shield volcanoes, has a shallow surface slope due to the low viscosity of the lava flows that formed it; however, the northwest shoreline boasts some of the highest seacliffs on earth. Events during and after its eruptions give the volcano several unique geomorphic features, some possibly resulting from the ancient collapse and landslide. The volcano is shaped like a foot; the northeast coast is prominently indented across of shoreline. There is a small string of faults on and near the main summit caldera, arranged parallel to the northern coast. The faults were originally regarded to be a direct result of the collapse; however scientists note the fault lines do not go all the way to the coast but are arranged tightly clustered around the caldera. This indicates that the fault lines may have been caused indirectly, possibly due to the sudden release of stress during the event. Hydrology Mauna Kea causes the trade winds to divert around it, increasing wind to super-enhanced flow over the Kohala ridge and orographic lift brings most of the rainfall to the northeastern slope of Kohala. The windward side of Kohala mountain is dissected by multiple, deeply eroded stream valleys in a southwest–northeast alignment, cutting into the flanks of the volcano. North of Kohala's summit the volcano's northwest–southeast trending rift zone separates rainfall into two streams, going southeast, into Waipio Valley, or northwest, into Honokane Nui Valley. When the volcano was still active, vertical sheets of magma, arranged in what is known as dikes, forced their way out of the magma reservoir and intruded into the rift