The Core Reason: Temperature Decreases with Altitude
Mountains often have snow on their tops because air temperature generally decreases significantly with increasing altitude. Even if the base of a mountain is warm, its summit can be high enough to reach temperatures consistently below freezing, allowing snow to accumulate and persist throughout the year.
Atmospheric Lapse Rate Explained
This phenomenon is primarily due to the atmospheric lapse rate, which describes the rate at which air temperature drops with elevation. As air rises, it expands due to lower atmospheric pressure and cools. If this cooling brings the air's temperature below the freezing point, any moisture present will condense and fall as snow.
Mount Kilimanjaro: A Tropical Snow-Cap Example
A striking example is Mount Kilimanjaro in Tanzania, located near the equator in a generally warm climate. Despite its tropical surroundings, the mountain's peak, towering over 19,000 feet (5,800 meters), remains permanently snow-capped because the extreme altitude ensures temperatures stay well below freezing.
Ecological and Hydrological Significance
The snow and ice accumulated on mountain tops are crucial. They form glaciers and snowpacks, acting as vital freshwater reservoirs that slowly release water as they melt. This meltwater feeds rivers and streams, supporting ecosystems, agriculture, and human populations downstream, especially in arid regions.