The Glacial Pace of Change

Glacial Timescale

The second major player in shaping the landscape has been a long series of glacial-scale geological processes. You can still see them operating in the high country, as the tiny remnant glaciers tear bowl-shaped valleys off the north facing slopes of the Olympics.

There is lots of debate about global warming and global cooling cycles. Suffice it to say we have ice-cores from the antarctic that go back thousands of years and we can examine the chemical content of water that fell as snow a very long time ago.

This frozen water has some interesting attributes that will reenter the story eventually: the ratio of carbon-12 to carbon-14 varies over time in CO2, but Oxygen has isotopes as well and these isotopes allow us to age-date water in certain kinds of aquifers rather accurately.

Anyway, until we get access to more complete data that's now emerging from melting ice near the poles, the beginning of our Glacier story starts here, above the Vashon lobe of the Cordillaran Ice Sheet barely 12,000 years ago:

You can still see deep grooves carved into the rocks on the back side of Mt Zion from when ice over Bon Jon Pass into the Little Quilcene River Drainage. In fact, one of the reasons we believe that the Little Quil provides such good drinking water is that it was protected from the sediment riding along the bottom the glacier by clean ice from the top of the glacier pouring down the drainage from above, and if you know your rocks (hint: the ones you are looking for are not basalt ...) you can trace the lateral and terminal moraines left behind by dozens of overlapping tongues of ice as the glacial ice advanced and receded.

One of the things this photographic reconstruction does not really communicate is that the rivers above 2500 feet were still flowing and their erosional processes were still running essentially as they do now except that the water they discharged did not return to the sea - instead it formed enormous fjords, and these fjords filled with sediments as well as boulders that were carried in icebergs that calved off the main ice-sheet and floated up the fjords. you may have seen them: huge boulders - some as big as you house, with trees growing on top.

You see them and climb up on top and you look up and wonder how much noise they must have made as they rolled down the valley and then it hits you: you realize the cliffs are all basalt and the boulder is all granite. Where did this thing come from?

It came from the Canadian coast range, carried south in the river of ice.

OK, now we have to get serious for a minute.

The ice was thousands of feet thick and water weighs over 62 pounds/cubic foot. Ice floats but even frozen water weighs more than 50 lbs/cf so that means 50 X 2000# of 50 X 3000# per square foot loading. Enough to deflect the earth's crust significantly! And to scarify the surface to a level that a bulldozer operator would be proud to have achieved.

The generally repeated fiction is that native Americans walked here from Asia across this sea of ice or walked across a land bridge that appeared as a result of fluctuations in sea level associated with the ice and the rebounding crust. Regardless of the route, there is plenty of archeological evidence to place them here when a lot of the landscape looked very much like this.
Regardless, there is pelnty of archeological evidence to place them here when a lot of the landscape still looked very much like this.

25,000 years 20,000 years 18,000 years 16,000 years 6000 years

Following the retreat of the ice, several things happened in sequence, the most important being revegatation, as shown beginning in the image.

Where did the plants come from? There were islands offshore that did not get buried under ice and they served as refugia for plants and animals.

The other critical thing that happend was that the salmon came baclk to their rivers. And fertilized the watersheds with their carcasses, making it possible for nature to revegatate the area rapidly. Within a few thousand years, there were forests again!

I wrote this almost 20 years ago, but the facts have not changed so it's still worth reading:

"Since that time (the retreat of the icesheet) the forested lands and the rivers that drain them, and the salmon that return to them year after year, have been developing together.

People have been here the whole time, and have left a telling record in their garbage dumps. We find them exposed in landslides and dig them up when we excavate the foundations of our homes: firepits and middens, the remains of the campsites the Indians left behind. We see another record in the pollen layers preserved in lake-bottoms and bogs.

This shows the pattern of forest fires, and the slow parade of flowering plants that gradually recolonized these mountains and shorelines. The salmon return from the sea to spawn and die, carrying back to the upper reaches of our rivers the richness of their bodies, ions of metals not found in the rocks of our mountains, proteins built from nitrogen and carbon, all collected during the years they spend foraging in the estuaries and oceans.

In the blind passion of their return they bring these nutrients from the sea back to the land and in their death they leave them behind, to be distributed into a vast food-web containing at least 22 vertebrate species. Nothing else in nature does this.

Every other natural process eventually depletes the land, drains its riches to the sea. The glaciers abrade it, the fires release it to the rain. The rain erodes it away and flushes it downstream, hurrying it back to the sea. It is very probable that in the wake of the retreating ice-sheet, the salmon prepared the barren mineral surface of the land for the forest we now see. Run after run of salmon fertilized the upper reaches of the streams and built up the nutrient supply until trees could take root and grow here.

The forests appear to be very young on the Olympic Peninsula. According to the records left by the Indians, the big trees have only returned during the last 3000 years, and some of them are over 1500 years old. After there were big trees, the people on the north coast could build boats and take to the sea themselves, and they hunted for seals and whales. Until then, they
lived off the land, off the salmon and deer, and other, smaller mammals.

The geology of the central Olympics is some of the most complex on earth, and defied mapping until the middle of this century. The mountains here are composed of uplifted layers of ancient sea-floor, of basalts from undersea volcanos and sediments deposited during 40,000,000 years of continental erosion. Some of these ancient sediments remain as shales and sandstones, others have been metamorphosed into slates and schists.

Each layer responds differently to erosion. About 15 million years ago, the material which became the Olympic Mountains was scooped off the bottom and slowly uplifted by a great ongoing collision. The horseshoe-shaped basalt crescent of mountains that flanks the peninsula on the north and east flanks, from near Neah Bay around the end of Discovery Bay to well south of the Skokomish River, represents the remains of a series of seamounts, great undersea volcanos, containing over 10,000 cubic miles of material.

These enormous basalt mountains became caught in the subduction zone, the area where the eastward advance of the sea-floor runs under the lip of the north-american subcontinent. Behind them, the sea-floor continued to advance and the crust, which is thinner at the bottom of the ocean than it is at the surface, buckled and broke into gigantic slabs, the advancing sea-floor sliding under each broken plate and tilting it on edge. This happened dozens if not hundreds of times and created a unique landscape: alternating layers of harder and softer rocks. Eventually, the subduction zone moved west, off the coast this entire tortured landscape floated above the surface, and in the process, folded like a strudel."

There are some really wonderful books about this, including my copy of Roland Tabor's book which is missing so I can't scan it (Tabor and Cady are the people who decoded the mystery of the geology) and you should read them, and then we can go for a walk down the ridge toward Lake Lillian and I can show you places where the a dozen layers of sedimentary rock are folded like strudel.

But that is not the real issue here: What is REALLY important about the glaciers is what they left behind. Which takes us to the discussion of erosion, saltation, bedload transport, aggradation, and that will explain WHY, after all these years, the fish that make nests in the lower reaches of our rivers are in so much trouble, and that will take us straight into the reason that this whole instream flow discussion is "suddenly" taking place.