NEARSHORE POCKMARK FIELD DYNAMICS AND EVOLUTION

NEARSHORE POCKMARK FIELD DYNAMICS AND EVOLUTION

By Laura Lee Brothers

Thesis Advisor: Dr. Joseph T. Kelley

An Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Earth Sciences)

August, 2010

Nearshore pockmarks are one the largest, most ubiquitous types of marine landforms in world, yet they are one of the least understood. These seafloor craters can be hundreds of meters in diameter, and may occur in fields of thousands. Questions persist regarding their origins, activity, how these fields evolve overtime and their potential role as geohazards.  To address these uncertainties we conducted geophysical, sedimentological, spatial, geotechnical, numerical and analog investigations of the Belfast Bay, Maine pockmark field. Stratigraphic analysis suggests that the field at one time was an environment rich in organic material, which could relate to the abundance of modern shallow gas in the field. We find that the pockmarks are non-randomly clustered and correspond to irregular underlying topography. The distribution of pockmarks within the field may relate to bedrock structural controls. Within our detection limits pockmark initiation appears to be an episodic, potentially catastrophic, event.  Once initiated pockmarks become scoured by nearbed currents. These currents may maintain and enlarge pockmarks.