Geology of Mukilteo

Geology of Mukilteo. Mulkilteo Walking Tour Stop 7. , Geology , The landscape you see from Lighthouse Park has been shaped by geologic processes. These processes have been working slowly and steadily over the past 2 million years of the Quaternany period, a long episode of creation and destruction. During this time, the older Olympic Mountains were eroding and the Puget Sound landscape was being formed, with its broad waters, distinctive islands, and coastal bluffs and beaches., Six glacial episodes have impacted Puget Sound. Each glacial episode included the southerly advance of glaciers from Canada, followed by melting and retreat to the north. The glaciers acted like bulldozers, carving the landscape and moving soil and rock ahead of them under the force of the moving ice and the water flowing beneath the ice. As the glaciers melted and retreated to the north, water flowing to the south eroded much of the material that had been emplaced during the glacial advance. The older soil deposits comprising the bluffs of Mukilteo were emplaced about 200,000 years ago during the Pleistocene period, with the youngest placed about 10,000 years ago., The most recent glacial episode, the Fraser Glaciation, lasted from about 25,000 to 10,000 years ago. When ice moving southward from Canada reached the Olympic Mountains, during the Vashon Stage of the Fraser Glaciation, it blocked the Puget Lowland and turned it into a large lake. Water flowing into the lowland filled the lake with clay and silt, then sand as the moving ice grew closer. The different types of soil deposits that can be seen in the bluffs to the south of Lighthouse Park reflect differing processes. The silt and clay were deposited in the quiet water of lakes while the coarser sand and gravel deposits were emplaced by higher energy flowing water. Large boulders that are occasionally found in the area, known as dropstones or glacial erratics, were rafted into place by ice masses floating in the inland sea or left in place as fixed ice melted., The landscape that we see today includes the remains of the sediment transported and deposited during the glacial advance. The open areas reflect erosion of these materials by water that flowed from the melting glaciers as it retreated and wasted away. Natural weathering processes, including landsliding and erosion, are ongoing and continue to alter the landscape., The currents of Puget Sound move sediment eroded from the uplands to form beaches. Wave action and currents or littoral drift in Puget Sound constantly move the sediments that form the beaches. This led to the creation of a sand spit many years ago at the site of Lighthouse Park. The embayment that was formerly present between the current beach and the bluff to the south of the Lighthouse was filled during development of the waterfront to make the level space that now comprises much of the park., MODERN TECHNOLOGY HELPS REVEAL OUR GEOLOGIC PAST. , [paragraph, timeline at bottom of marker, and map captions are illegible]