Discovery Park’s South Beach: Seattle: Lovely Geologic Beach Formation
South Beach and Mount Rainier by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License
South Beach and Mount Rainier: The mountain peaks from behind North Bluff at Discovery Park's South Peach. Photo taken April 7, 2012.
Seattle’s Discovery Park features numerous geologic processes, but sometimes the simplest are the most beautiful. South Beach is extraordinary. Puget Sound’s beaches started to form approximately 5,000 years ago, after sea levels began to stabilize in the region. Their material came from the higher elevation sources, such as the nearby hills and bluffs, and lahars produced by Mount Rainier. Much of the material was glacial till, which forms many of the taller landforms.
Several components form South Beach, from small sands to large boulders, all different materials. This is not surprising due to the vicinity of South Bluff, which looms over the landscape. Several layers of glacial deposits form it. Glacial debris comes from a variety of sources, all transported along the path of the continental ice sheet, which covered much of western North America. As it formed, it churned up the landscape, carrying enormous pieces of it. Some of these pieces were ground up during the journey, forming glacial flour (silts, clays and sands). Others remained gigantic. When the glaciers melted and receded, they dropped off the chunks. The layers in South Bluff form different episodes of the last glacial episode. These varied sands to boulders, all of a variety of origins, eroded downward, forming the beach.
South Beach’s variety of rocks and rock size diversify its landscape. However, other elements guide the formation. The slow movement of the water over the beach forms ripples. The differing directions of this movement forms crossed ripples. These ripples are mimicked in the pools of water between the rocks. The formation of pools and bars further influence the water speed, which alters the landscape. It is the same idea as a Catch 22. Higher areas act as barriers, slowing water down to some regions. At the same time, these same higher areas funnel water through channels, speeding up flow and depositing larger rocks. These are all visible in the photo at the top of this post and the short 13-second video below.
Discovery Park South Beach by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.
Discovery Park’s South Beach: Seattle: Lovely Geologic Beach Formation by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.