Hurricane Kay (September 2022) Impacts Rocky Shores in the Loreto Area of Baja California Sur, Mexico

Abstract

This project follows a tradition of survey work undertaken to appraise physical and biological damage in the aftermath of hurricane-strength winds and waves at a given locality where conditions were well documented prior to the arrival of a particular storm. The locality is the 12 m limestone terrace at Arroyo Blanco on the eastern shores of Isla del Carmen in Baja California Sur, Mexico. A study undertaken in February 2018 established that the surface of the terrace is covered by a coastal boulder deposit that features large slabs of limestone pealed from the outer edge by strong surf attributed to storms of hurricane intensity but unknown date. The largest slabs tend to be rectilinear in shape vulnerable to dislodgement along horizonal bedding planes and weaknesses in vertical joints. These blocks are sufficiently large and weigh enough that movement by humans without necessary mechanical equipment would be impossible. Hurricane Kay, rated as a Category 2 storm, struck the island on 8 September 2022 and an effort was made to visit the area for reconnaissance and detailed survey work soon afterwards. Although a Category 2 storm lacked the energy to remobilize the largest limestone slabs on the terrace, it was found that the storm was sufficient to disturb the adjacent seabed and redeposit as many as 44 sea fans onto the terrace by overwash; the sea fans belonged to the species Pacifigorgia adamsi. Moreover, a species of land plant common to the limestone terrace is the Gulf Star Violet (Stenotis mucronate); it suffered significant desiccation and death due to saltwater exposure. The occurrence of large potholes on the limestone terrace represents a style of physical erosion previously undocumented at the locality and rarely seen elsewhere on rocky shores.