Stunning tubular rock columns and sea caves － Wang Chau

Stunning tubular rock columns and sea caves － Wang Chau

Background Information

Wang Chau is the smallest amongst the Ung Kong Islands. The highest point is merely 80 metres above sea level while the narrowest part measures only 500 metres. It is a barren island with poor soil and hardly any vegetation. Geological sceneries, however, are enthralling. On the north side of Wang Chau one finds a striking sea cave. To see it in true grandeur, visit a few days after a typhoon when the ravaging ocean surge has subsided but the sea is still a little rough. On such days, swirling swells beat up a spectacular resonance in the cave, testifying to the mighty power of nature. Sea cave generally means a pit or trough carved out by waves and currents at the foot of a sea cliff. It is a type of wave-cut landform. Wave-cut action is the damaging impact, erosion and abrasion effect on a coast caused by waves and the sand, gravels and small stones they carry. This process occurs in three forms: erosion, abrasion and dissolution. Erosion is the washing impact of waves and currents on a coast. When waves hit against the rock surface, air in the bedrock cracks is compressed and imposes great pressure on the rock. When the swell subside, compressed air expands suddenly. This continuous process of abrupt contraction and expansion made the rock disintegrate. Abrasion is the impact, chiseling and grinding effect on the bedrock made by sea surge laden with lithic shards and sandy gravels. It accelerates the wave-cutting action. Dissolution means that rock is dissolved by seawater. While carbonate rocks are most vulnerable to dissolution, other rock minerals like orthoclase and amphibolite dissolve more than ten times quicker in seawater than in freshwater. Sea caves, sea cliffs, sea arches, sea stacks, wave-cut platforms and sea terraces are typical wave-cut landforms.

Geological Information

Like Bluff Island, the outcropped stratum of Wang Chau is part of the Early Cretaceous Kau Sai Chau Volcanic Group. Sea caves on the island are well developed. As a result of geological factors and sea level movements, they are greater in depth than width. Major geological factors include the types of shore-forming rocks or substances and their resistance to erosion, attitude of rock beddings, geological composition and crustal movement of the coastal region. These factors influence coastal characteristics and evolution to a great extent.