Chemical Weathering: Carbonation

• Carbonation


  A chemical weathering process. It is the process of rock being dissolved by a weak carbonic acid. Limestone is particularly affected by acid rain because of its characteristics.
• Characteristics of Limestone


  1. Limestone is a soft sedimentary rock. The shells of dead sea creatures (fossils) fell to the ocean floor. They mixed with sediment and built up in layers of rock called 'strata'.
  2. Each strata was separated by horizontal cracks called bedding planes. Each layer also has vertical cracks called joints.
  3. Bedding planes and joints make limestone permeable - water can pass through it.
  4. Limestone is composed of

  calcium carbonate because of

  the fossils it contains. Acid rain reacts with calcium carbonate and dissolves it.
• How carbonation weathers limestone

  1. As rain passes through the atmosphere, it combines with carbon dioxide to produce a weak carbonic acid.
  2. When acid rain falls on limestone, it dissolves the weaker parts of the limestone surface. These weaker parts deepen and form grikes over time. The slabs between the grikes are called clints. The pattern of clints and grikes makes up limestone pavement. Areas of bare limestone pavement are called karst landscapes.
• How carbonation weathers limestone Part 2

  3. Limestone is easily eroded by the weak acids found in river water. Eventually a river will erode down through the limestone. This creates a swallow hole. Sometimes a plunge pool is formed where the river meets the floor of the cave.

  4. As water moves through the joints and bedding place of the permeable limestone, it dissolves the calcium carbonate and can form underground features.