Journal of Marine Science and Engineering Article Geomorphology of a Holocene Hurricane Deposit Eroded from Rhyolite Sea Cliffs on Ensenada Almeja (Baja California Sur, Mexico) Markes E. Johnson 1,* , Rigoberto Guardado-France 2, Erlend M. Johnson 3 and Jorge Ledesma-Vázquez 2 1 Geosciences Department, Williams College, Williamstown, MA 01267, USA 2 Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada 22800, Baja California, Mexico;
[email protected] (R.G.-F.);
[email protected] (J.L.-V.) 3 Anthropology Department, Tulane University, New Orleans, LA 70018, USA;
[email protected] * Correspondence:
[email protected]; Tel.: +1-413-597-2329 Received: 22 May 2019; Accepted: 20 June 2019; Published: 22 June 2019 Abstract: This work advances research on the role of hurricanes in degrading the rocky coastline within Mexico’s Gulf of California, most commonly formed by widespread igneous rocks. Under evaluation is a distinct coastal boulder bed (CBB) derived from banded rhyolite with boulders arrayed in a partial-ring configuration against one side of the headland on Ensenada Almeja (Clam Bay) north of Loreto. Preconditions related to the thickness of rhyolite flows and vertical fissures that intersect the flows at right angles along with the specific gravity of banded rhyolite delimit the size, shape and weight of boulders in the Almeja CBB. Mathematical formulae are applied to calculate the wave height generated by storm surge impacting the headland. The average weight of the 25 largest boulders from a transect nearest the bedrock source amounts to 1200 kg but only 30% of the sample is estimated to exceed a full metric ton in weight.