Bullwings: Orcas Issues is proud to collaborate with the Stewardship Network of the San Juans to bring its series, “A Short Run to the Sea” to our readers.
We will reproduce daily articles from the series created and published on Stewardship Connections, an electronic publication of the San Juan County Marine Resources Committee and Lead Entity for Salmon Recovery.
We Call it “The Rock” For a Reason
“I’m going to be off the rock for a few days.”
“I can’t wait to get back on the rock.”
Yes, we often simplify the name of our beautiful home here to “the rock.” As it turns out, that’s a pretty accurate description of our islands’ geologic characteristics.
Repeated glaciations during the last ice age shaped the bedrock and developed the rugged landscape of the islands. Try to imagine that huge sheet of ice, over a mile thick, carving and polishing as it advanced, retreated and advanced again. The islands were completely overridden by glaciers and even the top of Mount Constitution was polished by glacial action. The glaciers carved out marine channels and scraped the resulting islands down to the bedrock
As the last glaciers melted, they left behind deposits of clay, silt, sand, gravel and boulders, especially in low-lying areas. But in the San Juans, these deposits are relatively thin when compared to other areas in Puget Sound, where this type of deposition may be several thousand feet thick. Contour maps of sediment thickness show most of the San Juans have less than 20 feet of sediment cover (White, 1994). Compared to the sediment layers in other parts of the Puget Lowland, this thickness is miniscule.
As time progressed, soils formed. Today, our islands are blanketed predominately with thin soils that sit atop either bedrock or layers of glacial “hard pan.” When contaminants from our daily lives are picked up in the rainwater these thin soils are limited in their natural ability to filter out the pollutants.
Most island residents (about 75% of us) get our drinking water from wells, and the majority of the wells in the County are located in bedrock. This groundwater comes from collected rainfall that works its way through many intersecting fractures in the bedrock. Because the water flows through cracks in the rock, there is little filtration. Even the wells that tap into glacial till aquifers are limited in their ability to filter contaminants. Considering we get only half the rain compared with most of western Washington, protecting the quality and quantity of our limited water supplies is critical.
To help keep our drinking water and the water that makes its way to our wetlands, ponds, streams and marine waters clean, we need to consider the reality that natural filtration processes are limited in the San Juans.
For the full series of articles, go to www.shortruntothesea.org
The San Juan Marine Resources Committee (MRC) was started in 1996 as a grassroots effort to establish local management of marine resources. It was the prototype for the creation of a federally sponsored network of seven MRCs working in northern Puget Sound and the Strait of Juan de Fuca. The MRCs are supported by federal funding through the Northwest Straits Marine Conservation Initiative.
The”Short Run to the Sea” campaign, has been supported by the Education, Communication and Outreach Network (ECONet) of the Puget Sound Partnership.
