Towards an improved understanding of erosion rates and tidal notch development on limestone coasts in the Tropics: 10 years of micro‐erosion meter measurements, Phang Nga Bay, Thailand

Knowledge and understanding of shore platform erosion and tidal notch development in the tropics and subtropics relies mainly on short-term studies conducted on recently deposited carbonate rocks, predominantly Holocene and Quaternary reef limestones and aeolianites. This paper presents erosion rates, measured over a 10 year period on notches and platforms developed on the Permian, Ratburi limestone at Phang Nga Bay, Thailand. In so doing it contributes to informing a particular knowledge gap in our understanding of the erosion dynamics of shore platform and tidal notch development in the tropics and subtropics – notch erosion rates on relatively hard, ancient limestones measured directly on the rock surface using a micro-erosion meter (MEM) over time periods of a decade or more. The average intertidal erosion rate of 0.231 mm/yr is lower than erosion rates measured over 2–3 years on recent, weaker carbonate rocks. Average erosion rates at Phang Nga vary according to location and site and are, in rank order from highest to lowest: Midplatform (0.324 mm/yr)>Notch floor (0.289 mm/yr)>Rear notch wall (0.228 mm/yr)>Lower platform (0.140 mm/yr)>Notch roof (0.107 mm/yr) and Supratidal (0.095 mm/yr). The micro-relief of the eroding rock surfaces in each of these positions exhibits marked differences that are seemingly associated with differences in dominant physical and bio-erosion processes. The results begin to help inform knowledge of longer term shore platform erosion dynamics, models of marine notch development and have implications for the use of marine notches as indicators of changes in sea level and the duration of past sea levels.