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Abigail B. Calkin

A Blog of Flashbacks

What Is Isostatic Rebound?

March 2020

There are many things I love about living in Alaska. One of my favorites is isostatic rebound. As the warming planet stares us in the face, our glaciers melt and sea level takes away some northwestern Alaska Native villages that have been there for at least 10,000 thousand years. I live in a different part of Alaska though, which is 1,500 miles southeast of them, but I hear of the changes that cause the people to make plans to move their entire villages. Where I live I see the changes to glaciers and land. I see land recently deglaciated and l live on land that was covered by a glacier a millennia ago. I live on land that had no recent human inhabitants just over 100 years ago. It was a glacial outcrop of only gravel and moisture. The oldest tree in the area is now not even 200 years old. I grew up in New England and areas around there. When one of my father’s scientist colleagues said to me when I was 14, “You are but a second in geologic time,” I was shocked, but my eyes opened wide from that moment forward. Until I moved to a town on Icy Strait, I was not used to daily thoughts about my life in geologic terms. Here we are quite familiar with isostatic rebound even if not with the term itself. What is isostatic rebound, other than a term I like for how it sounds? Its definition is the rise of a landmass that has been compressed by the weight of glacial ice for centuries if not millennia.

You may not be aware of this if you haven’t lived with oceans and glaciers for your neighbors for at least a few decades. Even in coastal New England, I wasn’t aware. At least part of Southeast Alaska, the part where I live between Skagway and the Fairweather Fishing Grounds of the Pacific Ocean, our land rises at about an inch to an inch and a half a year. This is due to isostatic rebound, the rebounding or rising of the earth when released from great pressure. About 20,000 years ago, there was a glacier that stretched from northeast of Skagway into the Pacific Ocean, a distance of about 250 miles. It also continued far east to the Rocky Mountains, a distance of about 2,000 miles—2,000 miles of mountain tops and icy glaciers. The sight of nothing but glacier and snow-covered mountains on a sunny flight between Juneau and Seattle is a sight well worth the airfare. In my area, the once-4,000-foot mass of glacial ice has now melted down to hundreds of feet at most. With the weight of tons of ice lifted from Earth’s surface, the land now rises.

A cubic foot of ice weighs 57.2 pounds. What does a 4000-vertical cubic foot of ice weigh? The answer is 228,800 pounds. One vertical square foot of ice weighs that much. Four thousand feet was the approximate height of the glacier and its per square foot on each square foot of the land was that 228,800 pounds. Certainly that weight will press land down. I sometimes lie on the Gustavus beach and picture I’m under 4,000 or even 1,000 feet of ice. I am a shell crushed into granules of sand. How broad was that mass of ice? Broad enough to cover almost all of North America, Europe, and the northern half of Russia. This occurred up until about 11,000 years ago.

Then from about 1400 to 1900, there was another Ice Age, this time called the Little Ice Age, which existed in various places including North America and Europe. Brian Fagan’s book, The Little Ice Age, gives an excellent description. He calls the land between Glacier Bay National Park and Yakutak the last remnant of this period. Yakutak, 150 miles away, is our closest neighboring town to the northwest. I fly over those 150 miles in awe. While our glaciers were much smaller in the Little Ice Age than in the end of the Wisconsin Age, they are even smaller now. Goodness, the Wisconsin Ice Age lasted from about 75,000 years ago to 11,000 years ago. I can imagine 11,000 years ago because I live on land where others lived then, whether in Alaska or the High Desert of southeastern Oregon. But 75,000 years ago? That is more than I can imagine. There were no residents of Alaska or Oregon’s High Desert then. I can picture back to 14,000 years ago when there were residents of Lake County, Oregon, and of Alaska. That’s as far as my thoughts stretch. I must learn to take them back further, before there were people in North America. Perhaps I need to imagine being a boulder or a mile-high mountain top in those days.

Why does this Earth-bound information deserve to be in my blog titled Flashbacks? Because the planet is changing whether we like it or not.  As snow melts, oceans increase in size. Oceans are warming too. Fish life is changing. The Pacific cod that used to be a local fishery for us are moving farther north to cooler waters for their livelihood and survival. Far south of us, coral reefs are endangered and disappearing partly due to human-caused reasons and partly due to independent world climate change. Renee Cho wrote an article worth reading on coral reefs in 2011, now updated as of 2018 (https://blogs.ei.columbia.edu/2011/06/13/losing-our-coral-reefs/). I live in the largest temperate rainforest on the planet. Coral reefs are the ocean’s equivalent to rainforests and they are at least as endangered as rainforests.

Planet Earth cannot speak a language any human directly understands. Couple that with the depths of our oceans that we cannot see. Sub-marine vehicles are not enough for it would be like looking at Kansas and saying that life in the nearby Colorado Rockies is the same. (I choose those two neighboring states because I’ve lived in both and know their stark differences.) Planet Earth is not panicked, or even worried or concerned about its changes and survival. It does not speak our language, but we must learn to understand it. We are doing a poor job at this. We can ignore all this at our own peril. Let us do better at looking before we and our planet change irrevocably. Our planet is not sentient, at least as far as we know. However, let us not become victims of change while living here.

I never lived anywhere where I can watch the earth around me change, that is, until I moved to Gustavus. Even today I watch the glaciers melt. For last 27 years I’ve taken the day-boat up-bay and I’ve taken a flight-see over the area and its glaciers. Every summer I take too many pictures of mountains and glaciers, but I can look at them and compare 1993 print photos to 2019 digital photos. When I now fly to Juneau in summer and see no snow on most of the Chilkat Mountains, I worry.

I watch the shoreline change, but that is probably due more to isostatic rebound than our land in trouble. Jack and Sally’s driveway used to flood at our highest tides of 20 feet. Since the land has risen by about a yard in my Gustavus lifetime, their driveway no longer floods. High tides at the beach 30 years ago used to flood the land back from the ocean but not anymore. I see a Gustavus coastline that has a three-foot dune between the dock and the Salmon River. There was no dune there 30 years ago.

I watch winters go from an expected 10- to 12-feet of snow down to a foot and a half for three winters in a row. This winter we are still short, maybe a 16-inch base instead of three feet or more. Winter has always been my favorite season because I love the snow and cold. Some winters now I feel as if I live in rainy Seattle, Eugene, or Edinburgh. I like watching geology in action. I like the isostatic rebound, but where are my cold winters?

When we had our 32-foot well dug, Bruce threw away the shells found at the bottom. Oh no, I wailed to my neighbor, Gary. He later had Bruce dig him a well at the same depth. Thoughtfully, Gary saved three shells from the dig on his land and gave them to me. I saved one and sent the other two to Beta Analytic, a lab for carbon dating analysis. The macoma baltica shell is about 2,400 to 2,550 years old. It cost me $600. My geologist brother thought I was silly to spend that money to analyze shells. Good heavens, Bill, you’re a geologist! It was not foolish but for science. I saved one shell to frame some day with a short story. I did it because it is the history of our land. I also wrote a poem about having “beachfront” property.

Salmon

When fishing for salmon you must consider
the time of year: catch fatty kings in the ocean of cold winter months,
when sensible fish and people gain fat to insulate in northern cold.
Catch sockeye when summer days grow short,
coho close to fall equinox when the moon shines full
and northern lights glimmer.
While you catch sockeye and coho, consider their stream.
Picture their source as they struggle up river against the flow to lay
millions of eggs so a few survive.
When catching fish as you stand on deck or bank,
consider the currents, the channels where they swim.
Consider the water’s temperature, the small canyons, rocks, and greens below.

Where do the salmon go these years?

They follow the currents to their food
every year arrive off their origin’s coast till,
mature, return to swim back, spawn, and die.

How do they know their way?

The waters of each stream hold a unique taste, smell, and
chemistry imprinted on young fry before they swam
to ocean those four years ago. Now that stream awaits their return.

What makes some swim to a new stream, a manmade ditch alongside
the road that holds pinks and now too cohos?
Why, how, did they change their pattern?
Who was the grandmother fish, who said
Now we will spawn here?

I live on a muskeg, an unromantic glacial outwash plain—
four inches of soil lie atop sand lie atop gravel, lie atop sand till
ten meters below lie macoma baltica shells on yesterday’s beach.
Today’s beach is three miles south. It is these shells that tell me
2,500 years ago when Socrates orated, Plato wrote, and the first democracy flourished,
this was beachfront property.
I rock on my deck and ponder that,
hear, feel the waves against the shore beneath my feet.
To inhabit the boggy terrain, men dug ditches,
drained the muskeg—sort of. We built houses and a town here.
The land rose because the glaciers retreated—isostatic
rebound they call it…and the ditches turned to streams that
carried the salmon past my cabin in the woods as they
made their ways into new channels into deeper streams holding
the right smells, tastes, and chemistry

until ten years ago I saw pinks in the stream and three years later more
pinks till now I see pinks and cohos every autumn in the stream
alongside the road.

I stop. Admire their struggle to pass even a four-inch terrain change.
I lean over, ask Where did you come from, my glistening silvery friend?
What part of the sea were you in while you were gone?
The waters of Mystic Islands? Cross Sound? The Fairweather Grounds?
The Washing Machine of South Inian Pass?
Why did you choose this tributary? What
is in your skin, flesh, and bones? What is it
you smell and taste that brings your offspring
back to my paths each year?

Last night I dreamed eggs began to hatch.
But it’s January! I say. Already you’ve
grown to four inches for your journey to the sea.
But you should still be fry! You wiggled a look at me
as if I, too, were under water, then continued your life’s journey.

I still open the little round Ukrainian box where my macoma baltica shell is and marvel at my once beachfront property and the isostatic rebound that has raised my land to 39 feet above sea level.

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