Abstract

The Mona Canyon off the northwestern coast of Puerto Rico has historically been considered a submarine canyon. Using a combination of Hydrosweep bathymetry, HMR1 sidescan sonar imagery, and reflection seismic data to examine the morphology and structure of the canyon in pseudo three-dimensions, this study presents evidence that that it is a tectonically controlled rift. The data show that the canyon is 120 km long and 20 km wide with a sinuosity of 1.21. It is divided into an upper and lower slope province, with the lower province having a higher gradient than the upper province. There is an overall depth change from 1 km to 7.5 km from the start of the upper slope to the end of the lower slope. In across-axis profile, the east wall of the canyon is steeper than the west wall for most of the length of the canyon. There is mass wasting along the sides of the canyon creating turbidite deposits in the canyon that are thicker in the upper slope section than in the lower slope section.

Four possible models for the canyon’s origins were considered; a formation by erosion hypothesis, a rotating blocks creating rifting hypothesis, a resistance to subduction creating rifting hypothesis, and a pull-apart basin hypothesis. Due to the presence, location, and type of active faults, it is determined that the canyon is indeed a rift, and the most likely result of the differential eastward velocity of Puerto Rico relative to Hispaniola.