Marine geologist Gary Greene will treat islanders to an absorbing visual tour of the hidden subsea world around the San Juan Archipelago, showing the strikingly beautiful sonar images he has been recording for the past 20 years.

This Orcas Currents lecture is on Thursday, June 11 and is cosponsored by Coates Vineyards and the Northwest Straits Foundation. It begins at 5:30 p.m. in Orcas Center, with a reception to follow sponsored by the Orcas Food Coop. Admission is free.

Formerly the director of the Moss Landing Marine Labs on Monterey Bay in California and currently a research faculty member at Friday Harbor Labs, Greene has pioneered sophisticated sonar techniques to map the sea floor in many regions of the Pacific Ocean. Now working with the SeaDoc Society and heading its Tombolo Mapping Lab on Orcas Island, he has been making high-resolution 3D images of the Salish Sea floor.

In the process, he has uncovered previously unknown benthic habitats and discovered geological features such as submarine faults and folding.

In his talk, Greene will bring alive the deep undersea world around us. Greene has also discovered an important new geological fault he dubbed the Skipjack Fault, which begins near South Pender Island and extends eastward to pass between Orcas and Sucia Islands.