Geology and Climate
Maunakea is a shield volcano, the third oldest and highest of the five volcanoes composing the Island of Hawaiʻi. Maunakea is estimated to be between 600,000 and 1.5 million years old, and is considered by the U.S. Geological Survey to be geologically active, and such is monitored as it is plausible it will erupt again on a geologic timeframe (US Volcanoes and Current Activity Alerts).
The formation of cinder cones, the movement of ice sheets, and the interaction of lava and ice has shaped much of the summit area. Between about 180,000 years ago and the present time the summit of Maunakea experienced at least three episodes of glaciation. Evidence of these glacial events includes till and moraines, glacially polished rock surfaces, lava-ice contact zones, and hydrologic features such as Pōhakuloa Gulch. Periods of recent volcanism also coincided with the presence of glaciers on the upper mountain. Lava and ice interaction is responsible for the lava outcrops associated with the adze quarries.
At the upper elevations of Maunakea, typical conditions are dry and cool, with excellent visibility and intense solar radiation. This combination allows the ground surface to warm, which has the effect of increasing evaporation of water and making plant establishment difficult.
At about 7,000 ft (2,133 m), however, when the trade winds are blowing, an inversion limits upward migration of the clouds, and above this level rainfall decreases with elevation, keeping Maunakea dry and cool from roughly 7,000 ft ( 2,133 m) upwards. Large storms may break through this inversion, occassionally depositing snow on the summit.