Ultramafic
Rock that is rich in magnesium and iron content.
Unconscious
Interruption of awareness of oneself and one’s surroundings, lack of the ability to notice or respond to stimuli in the environment. A person may become unconscious due to oxygen deprivation, shock, or injury.
Understory
The level of the rain forest just below the canopy.
Updraft
Upward movement of air.
Updrift (ocean)
The direction opposite that of the predominant movement of sediment along the shore. The side of a groin, jetty or other structure where sand accumulates.
Upland
A general term for land or ground that is higher than the floodplain.
Upper Mandible
Upper part of the bill.
Uprush (ocean)
The landward flow of water up onto the beach that occurs when a wave breaks.
Upstream
The direction toward a river’s source; opposite to the rivers’ flow.
Upwelling
The movement of nutrient-rich deep seawater to the ocean’s surface.
UV Degradation
A breaking down of material due to the sun’s harsh ultraviolet rays. UV degradation can be a potential problem with tent flies exposed to the sun for extended periods.