Monitoring Vertical Cliffs, Embayments and Shore Platform Morphology in Parts of Neil Island, South Andaman using Spatial Information Technology

摘要

The southern shores of Neil Island are fringed with vertical cliffs, embayments and near horizontal platforms on the rocky coast of windward side dominated by limestones, calcareous siltstones and biocalcarenites. The uppermost shell limestones, massive limestones and coralline limestones (Neil formation) are unconformably lying over the calcareous siltstones and limestones with ash layers in this part of the sequence ( Archipelago Group). Sequences of erosional landforms such as caves, notches, arches, stacks, geos. rockfalls and solution pits have been appeared to offer insight into the pattern of progressive change on the cliffed coastline of the island. The height of the cliffs ranges from 8-21 meters along the shoreline and they appear to represent successive stages of erosion that produced small embayments, bays and coves in between the resistant headlands. The wave attack on headlands, water layer weathering, successive wetting and drying and having presence with sufficient zones of weakness into the near vertical slopes of the cliff are the main causes for the gradual change in morphology. At the base of cliffs in entire parts of the island, near horizontal shore platforms are well developed within the intertidal zone ranging between 30 - 100 meters in width and extended seaward upto the margins of coral bank with descending slope The rate of cliff retreat and its spatial diversity as well as the resultant shoreline types are estimated with the LANDSAT ETM+ images of 2005 and 2015 for the above study. However, the morphology of shore platforms and cliffs is studied with the delineation of features from satellite images and temporal field verifications over the period between 2014 and 2017. The study reveals the nature of shoreline morphodynamics of the cliffed coasts of limestone rocks in the oceanic island.