In what type of terrain would you expect to find sinkholes, long dry valleys and disappearing streams?

• A. Karst
• B. Volcanic plateau
• C. Mountainous tundra
• D. Alluvial fan plain

Answer: (A)

Sinkholes, long dry valleys, and disappearing streams are hallmarks of karst terrain. This type forms where rocks like limestone or dolomite are soluble in slightly acidic groundwater. As water percolates through the soil, it dissolves the rock, creating underground voids and cave systems. When these voids grow too large or the overlying rock becomes unstable, surface collapse occurs, producing sinkholes. Water also tends to drain through the underground conduits, so streams may vanish from the surface as they disappear into the subsurface, then reemerge later as springs elsewhere. Over time, this dissolution and subsurface drainage carve out long dry valleys that carry little or no flowing water, with steep, rugged profiles.

Volcanic plateau, mountainous tundra, and alluvial fan plain don’t emphasize dissolution of soluble rocks and underground drainage in the same way: volcanic plateaus are shaped by lava flows, tundra landscapes are dominated by cold-weather processes and permafrost, and alluvial fans are built from sediment deposition at channel mouths rather than extensive subterranean dissolution.