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.
The Māmane woodlands once stretched from sea level on the leeward side of Maunakea to the tree line, but have been greatly reduced due to habitat alteration at lower elevations and uncontrolled grazing at higher elevations by feral sheep (Ovis aries), mouflon sheep (O. musimon), and goats (Capra hircus). Populations of Maunakea silversword have been drastically reduced by ungulate grazing. Although attempts have been made to control such grazing, the forest has not fully recovered due to continued browsing of ungulates and the presence of invasive plants that inhibit Māmane regeneration.Invasive Plants
Invasive plants include common mullein (Verbascum thapsus), fireweed (Senecio madagascariensis), ripgut brome (Bromus diandrus), orchardgrass (Dactylis glomerata), hairy cats-ear (Hypochoeris radicata), alfilaria (Erodium cicutarium), sheep sorrel (Rumex acetosella), common groundsel (Senecio vulgaris), common dandelion (Taraxacum officinale), and telegraph plant (Heterotheca grandiflora). Invasive plant species pose a great threat to native species because they compete with native species for limited resources such as water and sheltered growing locations, tend to reproduce faster than native species, and provide habitat for other non-native species such as insects.
Invasive Birds and Small Mammals
Maunakea is also home to many species of non-native birds and mammals. Invasive predators such as cats, rats, barn owls, and mongoose have a direct impact on native bird populations. Cats and mongoose eat both adult birds and chicks, while rats primarily consume eggs (and sometimes chicks). Non-native birds compete with native birds for resources such as food and can act as a food base for predators, which consume both native birds in addition to non-native species.