Explain the evolution of valley sinks or uvalas.
Valley sinks or Uvalas are formed when sink holes and dolines join together. This joining occurs through two main processes: slumping of materials along the margins of these depressions, or due to roof collapse of caves located underground.
As these sink holes and dolines combine, they create long, narrow to wide trenches which are termed as valley sinks or Uvalas. Gradually, the limestone surface gets eaten away by these pits and trenches, leaving behind an extremely irregular surface characterized by a maze of points, grooves, and ridges or lapies.
Explanation
The textbook explains the evolution of valley sinks or uvalas as a process where existing sink holes and dolines merge together. The key mechanisms are: (1) slumping of materials along the margins of these depressions, and (2) roof collapse of underground caves. The result is the formation of long trenches - either narrow or wide - called valley sinks or uvalas. This is part of the karst landform development in limestone regions.