Which of the following is classified as a constructive force?

Volcanic eruptions are classified as a constructive force because they contribute to the creation of new landforms and the addition of new materials to the Earth's surface. When a volcano erupts, magma from beneath the Earth's crust is expelled and, once it cools, forms solid rock that adds to the landscape. This process can build volcanic islands, mountains, and plateaus, significantly altering the terrain.

In contrast, the other processes listed tend to be destructive or erosive. Earthquakes, while they can create new geological features over long periods, primarily result in the destruction of existing structures and landscapes. Weathering involves the breakdown and alteration of rocks and minerals without transport, leading to surface loss or degradation rather than building up new land. Flooding can reshape land by erosion and sediment deposition but is generally more associated with the removal of materials rather than the formation of new ones. Thus, the active creation of land through volcanic activity is a clear example of a constructive force.