There are no birds in this Bucket. If you’re expecting birds here, my apologies. But please do add birds in the comments. This Bucket is about rocks, glaciers, and earth history. No rocks were harmed, though a few small, colorful, wave-polished cobbles found their way back to our house.
THE DAILY BUCKET IS A NATURE REFUGE. WE AMICABLY DISCUSS
ANIMALS, WEATHER, CLIMATE, SOIL, PLANTS, WATERS AND NOTE LIFE’S PATTERNS.
WE INVITE YOU TO NOTE WHAT YOU ARE SEEING AROUND YOU IN YOUR OWN PART OF THE WORLD,
AND TO SHARE YOUR OBSERVATIONS IN THE COMMENTS BELOW.
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About a month ago, my wife and I and our two dogs visited Barnum Point on Camano Island. Camano Island and its bigger sister island, Whidbey Island to the west, together make up Island County. Camano Island is named for 18th century Spanish explorer Jacinto Caamaño who explored much of the Pacific Northwest coastline. The indigenous Snohomish people know it as Kal-lut-chin which roughly translates to "land jutting into a bay".
Our routine for a day out starts with a hearty breakfast. This day was no exception as we paused in Silvana for breakfast at Willow & Jim’s Country Café.
Fortified we drove over to Camano Island and started our walk at Barnum Point County Park. Here’s the trail map displayed at the gravel-paved parking lot:
The Beach Trail courses through a mature forest of mainly Douglas fir ending on the beach. The ability to beach walk along Puget Sound shorelines backed by bluffs is subject to the whim of tides. We were in luck that it was an outgoing tide. There were still driftwood logs to negotiate. The beach is cobble shingle beach making footing less than firm.
Well, let’s look at the bluff and see what it tells us about the ice age, specifically the last advance of the Puget Lobe of the Cordilleran ice sheet. This last advance of the Puget lobe is known as the Vashon stade.
Once the ice sheet reached this area, the ice at its peak was about 4,000 feet thick. That is a considerable mass of ice pressing down on the surface, not only pressing down but moving at a glacial pace (135 meters / 443 feet per year). The weight and movement created the till layer (Vashon till) that you see at the top of the bluff. Till is a non-sorted, non-stratified material that was deposited or “smeared” beneath the sole of the glacial ice. It is dense to very dense and contains a mixture of clay, silt, sand, and gravel. It resembles concrete and is almost as hard.
The following map is a cartoon rendering of the geology at Barnum Point. You can view the whole map and descriptions here:
Geologic map of the Juniper Beach 7.5-minute quadrangle, Island and Snohomish Counties, Washington
So, the last big ice sheet advance was the Vashon stade where the Puget Lobe pushed down all the way to around Olympia about 15.000 years ago. When the Puget Lobe receded, the land had been depressed under the weight of the ice, depressed below sea level so the land was covered by marine waters as the ice sheet receded. When the ice sheet melted, the weight was lifted and the land surface rebounded. As the land surface rose above sea level, strand lines (beaches) formed as shown by the three purple lines on the geologic map. The other thing that was happening was the ice sheet and icebergs were floating around on a shallow sea. As the ice sheet and ice bergs melted, they were dropping silt and stones (“drop stones”) that had been picked up along the way as the ice sheet advanced. That’s how the Everson glaciomarine drift (Qdme) was formed, a build up of silt on the seafloor that shed from the melting ice.
Let’s look at some of these drop stones we found along the beach that the ice sheet transported in some cases way more than one hundred miles from their original location (provenance).
Next up is a chert-pebble conglomerate.
That’s it for beach boulder bingo. Let’s walk back along the Bluff Trail.
The dogs get thirsty after a long walk.
That’s all I have for today. What’s going on in your natural worlds?
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