Whidbey Island State Parks
Windows Into The Glaciers of Puget Sound
The two islands that comprise Island County (Whidbey and Camano) were shaped by multiple advances of glaciers from Canada over a period of two million years. The sediments left behind by those glaciers and the sediment-laden outwash from them is 250 to 800 meters (800 to 2,600 feet) thick below Whidbey Island, but thinning northward toward Deception Pass, where the underlying bedrock is exposed.
17,000 years ago, along the west coast of North America, the last continental glaciation extended south from British Columbia into the Puget Sound lowland, reaching as far as what is now Seattle. Ice covered the region for about 1,000 years, then began to melt and retreat.
Very Cool Animation!
by Ralph Haugerud
The ice thickness near Coupeville was 1,200 meters
(3,900 feet). The weight of ice on what was to become Whidbey Island was about 576 billion tons and depressed the land (the Earth's crust is flexible and responds to overlying masses like the glaciers). At the same time the growth of glaciers caused a lowering of global sea level with water locked up in glacial ice. The combination of lowered sea level and depressed land placed the island about 150 meters (500 feet) below what is today's sea level.
With a warming climate the glaciers' terminus began to recede northward at 340 meters (1,100 feet) per year. As the glaciers melted the land surface rose (rebounded) and sea level simultaneously rose. On Whidbey Island the rate of rising land exceeded that of the rising sea and as it rose, terraces were cut into the land by waves; the terraces are now visible around the island like bathtub rings.
Relief Map of Island County Washington
With State Parks and Other Parks
The most evident features are the north-south-oriented drumlins on Camano Island and the southern two-thirds of Whidbey Island. Drumlins are elongate hills of packed glacial till that were sculpted by the south-flowing ice. Drumlins can be seen in cross-section along Double Bluff Beach. Less developed northeast-southwest drumlins on north Whidbey (northeast of Oak Harbor) were formed when later movement of the glaciers went toward the Strait of Juan de Fuca.
From Crockett Lake to the northern shore of Penn Cove are features left by a stagnant ice front and higher sea level. These features include Ebey’s Prairie, which was formed by river deltas from melting ice that were constructed into a shallow sea (now Ebey's Prairie), and kettles in the Kettles Park and Fort Ebey State Park.
The northern tip of Whidbey Island, in Deception Pass State Park, is older bedrock that was eroded by the glaciers.
The largest erosional features are now flooded by the sea —Saratoga Passage, Holmes Harbor, and Admiralty Inlet.
Maximum advance of the last glaciation across southwestern British Columbia and northwestern Washington. Arrows indicate ice flow from the adjacent mountains and along the Strait of Georgia. Ice covered the region for about 1000 years. (from Porter and Swanson, 1998)