Life on the Edge

A Sound is Born
July 2008
by Nancy Sefton

Some folks from outside this area are geographically challenged when it comes to Western Washington. They think Seattle is perched right on the Pacific coast. Of course, WE know that we live around Puget Sound; the ocean itself is over 90 miles due west, far away across the Olympic peaks.

Imagine being around 17,000 years ago, when one could have walked across the Sound (no waiting in ferry lines). Back then, a great ice sheet had invaded from Canada to cover our entire region. At its toe, near present day Shelton, the ice rose 800 feet above a moraine. The future Olympia was covered by 1,500 feet of ice. Where Tacoma sits, the ice wall rose 2,500 feet. And Seattle? Over 3,000 feet of ice blanketed today’s busy metropolis.

This so-called Puget Lobe basically filled in the low areas between the Olympic and Cascade ranges, while a second lobe (not shown in the picture) pushed between Vancouver Island and the Olympic Peninsula, out to the Pacific Ocean.

But a big thaw was on the way. The ice sheet ultimately retreated, exposing deep gouges carved by ice and captured boulders grinding away relentlessly at the terrain beneath. Soon the Pacific Ocean poured in through the Strait of Juan de Fuca. Meandering trenches filled in to become greater Puget Sound, Hood Canal, and all those narrow passages so well traveled today by ferries, tankers, fishing boats, cruise ships and pleasure craft.

The great ice sheet left massive amounts of sediment behind. A great freshwater glacial lake, glacial meltwater and the glacier itself left layers of clay, sand and unsorted till respectively. As a result, the movement of sand and mud along our shorelines influences the kind of beaches we see today. Where steep bluffs are located, sandy beaches are constantly replenished by material shed from above. The often muddy bottoms of estuaries, where rivers enter the Sound, are replenished by sediments washed down from nearby mountains.

Because thousands of rivers and creeks pump fresh water into the Sound and saltwater pours in over shallow sills, the Sound itself can be considered a huge estuary, a big mixing bowl of fresh and salt water. It’s also referred to as an “inland sea”. Whatever the name, Puget Sound is a unique marine environment that deserves our most careful stewardship.