What term refers to a large mass of snow, ice, soil, rock, or mixtures that falls or flows rapidly due to gravity?

The term that describes a large mass of snow, ice, soil, rock, or mixtures that falls or flows rapidly due to gravity is "avalanche." Avalanches specifically refer to the rapid movement of snow and ice, typically occurring on slopes when the weight of accumulated snow exceeds the strength of the underlying surface. This term captures the unique characteristics of such events, which can vary in composition but predominantly involve snow and ice.

In contrast, the other terms refer to different types of mass movements. A landslide generally involves the sliding down of earth materials on a slope but does not specifically include snow or ice, which distinguishes it from an avalanche. A debris flow consists of a mixture of water and loose materials such as soil, rock fragments, or vegetation that flows down slopes, but again, it does not primarily involve snow or ice. Meanwhile, a rockslide is a specific type of landslide that involves the sudden fall of rock down a slope without the associations of ice or snow. Each of these terms refers to distinct geological processes, and the defining factors of "avalanche" make it the most appropriate choice for this question.