The karst topography is formed by the actions of

Ground water

Explanation:

Karst topography is formed when the underground water breaks down the bedrock into soluble rocks. Hence, the bedrock of Karst topography is made of soluble rocks such as limestone. There is no surface water and topsoil in this topography and hence, the water from rains become part of the groundwater.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.

when it is at an intermediate population density