The Fraser Glaciation was a glacial period that lasted from about 29,000 to 10,000 years ago. Toward the end of this period, about 13,000 years ago, streams from the retreating glaciers deposited sediment (sand, gravel and rock) and formed the Colwood Delta (see diagram below). This gravel sediment was mined for several decades starting in the early 1900s in the Metchosin gravel pit. A huge chunk of ice about 100 m thick became isolated from the main ice sheets, and gradually melted and formed Esquimalt Lagoon. Glacial sediments deposited around the ice block created the barrier spit now known as Coburg Peninsula, in a process described below.
Colwood Delta (used with permission, from Yorath and Nasmith, 1995) (1)
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As sand eroded from the Colwood Delta deposits to the south, it was transported northeast by longshore currents and deposited in front of the ice block. Longshore currents are created by waves that contact the shoreline on an angle and flow parallel to the shore (see coastal sediment processes
). After the ice completely melted a depression was left behind, and the rising sea level flooded the area that was to later become Esquimalt Lagoon. Longshore currents continued to build and stabilize the spit (Coburg Peninsula). Studies have indicated that before gravel mining operations began in the area to the south in the early 1900s, coarser sediment (i.e. gravel) probably predominated on the spit. Over the years, fine sediment that was spilled at the gravel loading docks has been transported to the north, resulting in a sandy beach along the spit.
Currently, a housing development is planned for the site of the former gravel pit at Royal Bay, which was decommissioned in 2007. This is expected to change the sediment regime of nearby shorelines, and result in a return to coarser, narrow beaches. Although this is the natural historical condition of the shoreline, the change will have impacts on the ecology of Esquimalt Lagoon.
(1) Yorath, C. J. and H. W. Nasmith, 1995. The Geology of Southern Vancouver Island: A Field Guide. Orca Book Publishers