Resumen de Rock coast erosional forms (notches and shore platforms) on the La Paz Peninsula, Southern Baja, Mexico
Alan S. Trenhaile, K. Prestanski, N.I. Porter, J. Gagnon
Changes in wave exposure produce a transition from various types of high tidal notches to narrow shore platforms in andesitic lahar deposits on the La Paz Peninsula, Mexico. Notches were surveyed in 18 areas. Thirty-six transverse micro-erosion meter (TMEM) stations were installed on three surveyed platforms. Laboratory experiments and analyses helped to determine processes and rates of notch erosion. Field measurements were made over 2.5 years and the experiments ran for 17 months. Erosion rates in the laboratory were about 1.80 mm yr-1 and 0.39 mm yr-1 in salt and fresh water, respectively. The narrow shore platforms (few tens of metres) reflected a weak wave environment and resistant rocks. Mean TMEM down wearing rates were 0.14 - 0.42 mm yr-1. There was a good relationship between notch height and wave exposure, but the relationship between notch depth with exposure was not statistically significant. Notch height was also related to the orientation and wave fetch of the site. Laboratory and field data suggested that the notches were produced by high tidal salt weathering. Erosion rates compensate for uplift rates of 0.12 - 0.15 mm yr -1, and coastal morphology is well adjusted to the present level of the sea.
