What process, along with erosion and deposition, significantly alters the landscape?

The process that significantly alters the landscape, in conjunction with erosion and deposition, is plate tectonics. This geological phenomenon involves the movement of the Earth's lithospheric plates over the semi-fluid asthenosphere. As these plates interact with one another, they can lead to the formation of mountains, ocean basins, earthquakes, and other significant geological features.

Plate tectonics shapes the Earth’s surface over millions of years, resulting in dramatic changes to landscapes. For example, the collision of tectonic plates can cause the uplift of mountain ranges, while divergent boundaries can create new oceanic crust. This continual movement and interaction not only affect topography but also influence climate patterns and ecosystems.

While volcanism is a notable process that can lead to temporary changes in landscapes—such as the formation of new land through lava flows—it is ultimately a subset of the larger dynamics involved in plate tectonics. Climate change and weathering also play significant roles in shaping the Earth's surface, but they do so primarily through surface processes and atmospheric influences, rather than the deep geological actions and tectonic movements that drive significant alterations in the landscape.