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Space Topics: Planetary AnalogsStars Above, Earth BelowAstronomy and Space Exploration in America's National Parks
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Glacial Valley Signs of past glaciation are everywhere one looks in the Many Glacier area of Glacier National Park. Note the U-shaped valleys with steep canyon walls. Credit: Tyler Nordgren |
Ex-Glacier Park
Glacier National Park, Montana -- As you drive up the
Swiftcurrent Valley to the Many Glacier area of Glacier National Park,
the evidence for enormous glaciation is all around. The valley has the
characteristic U-shape caused by the thousands of feet of flowing ice steadily
scraping the rock below it. On either side of the valley’s
entrance are hundred-foot-tall ridges running out of the mountains along
Lake Sherburne. These are lateral moraines, enormous depositories for all
that rock that used to be mountains. Above the lake on the northern mountain
wall are numerous hanging valleys, shallower U-shaped valleys made by smaller
glaciers flowing into the central glacier. Since they were smaller glaciers
they didn’t carve as deep. As a result, when all the glaciers receded
a hundred-foot drop into the main chasm remained behind. Farther
up each glacial valley at the end walls are the great circular basins where
the snows accumulated year after year to begin the process of glaciation.
In these cirques, the weight of all that accumulated ice compressed the
snow crystals at the bottom into flat sheets, allowing them to slowly slide
downhill to begin the mountain grinding in the first place. These are the
features on display in valley after valley of Glacier National Park, and
they give these mountains their unmistakable beauty.
Those giant Pleistocene glaciers have been gone for about ten thousand years,
but like the mastodon and saber-tooth tiger, they have left smaller descendants
that are disappearing today. On Tuesday I took a ranger naturalist-led hike
up to Grinnell Glacier, one of the last remaining glaciers. Along the way,
at an elevation of nearly a thousand feet above the glacial valley floor, I
found myself thinking about Mars.
The Grinnell trail passes through a layer of red rock called argillite. Argillite
is a sedimentary rock formed from the compression of successive layers of iron-rich
mud. Because this entire area was once a shallow sea, the iron hematite in
the rocks turned the red color we associate with rust and the planet Mars.
Fossil ripples Ancient ripples in the mud of a shallow sea are preserved in the red rock of the Grinnell Formation within the canyon walls of Glacier National Park. Credit: Tyler Nordgren |
Over the course of three miles and a thousand feet of elevation gain, I crossed through layer after layer of argillite on my way up the valley. In numerous outcrops, I saw the fossilized remains of water ripples and ancient cracks baked into the mud by the hot sun. Whatever sea was here was so shallow that the mud I walked upon was, over the years, alternately awash in flowing water and then left high and dry under a young sun. The red layers alternated with green layers, which formed from mud laid down in times of deeper water, in which the iron couldn't oxidize.
These are conditions probably similar in rough outline to those at Meridiani Planum where the Opportunity rover has found evidence of flowing water in what is thought to have been shallow seas or lakes. Just as I can read the Glacier region’s history in the mountain wall’s alternating stacks of red and green layers, planetary scientists can read the layers exposed in Meridiani’s crater walls to piece together its aquatic history. The similarity to Mars, however, doesn’t end with just the color of the rocks, but rather extends to the valley itself. Three weeks ago I chatted with Jeff Kargel of the University of Arizona about the evidence for ancient glaciation on Mars. He described to me how in a couple of forthcoming papers of which he is an author, orbital images of Mars show exactly the same types of features I see around me right now: U-shaped valleys, moraines, hanging valleys and cirques. A Martian glacier park is up there waiting for hikers of its own.
Evidence indicates that at some point during the past, the climate on Mars was such that water fell from the sky in one form or another, and glaciers formed and flowed across its surface. But Mars’ climate changed. Its glaciers dried up and probably evaporated as the atmosphere thinned and the planet cooled. Jeff describes much of the evidence for this early Mars in his popular book, A Warmer, Wetter Planet. Mars died. Climates changed.
It happened there naturally. It has happened here naturally. Dramatic climate change is all too possible. Read Carl Sagan’s Cosmos. In Chapter 5, Blues for a Red Planet, he describes how one could go about terraforming Mars: turning Mars’ climate back to its presumably warmer, wetter past. The key is to warm the planet by increasing the concentration of greenhouse gasses in its atmosphere. Sagan suggests seeding the polar caps with dark plant life that will absorb solar energy instead of reflecting it. In this way one heats the polar caps. Melt the frozen snows and one puts more greenhouse gases into the atmosphere, warming the surface even more. Repeat the process and over time the feedback mechanism yields the warmer, wetter, more Earth-like Mars like it once was. Such an undertaking would take enormous amounts of time and surely would be the most closely monitored and controlled scientific and engineering endeavor in human history.
Grinnell Glacier in 1900 and 1998
Views of Salamander and Grinnell Glaciers in 1990 and 1998. Credit: Matthes (Glacier NP Archives) and McKeon (USGS) |
Grinnell Glacier in 2007
The view of Salamander and Grinnell Glaciers photographed in 2007 from as near as possible to the original photos of 1900 and 1998. Credit: Tyler Nordgren |
Today, ironically, everything we would do to Mars, we are currently doing to the Earth, yet we are doing it to a planet that is already warm and wet and we are doing it in a manner with absolutely no monitoring or control. According to the folks at the U.S. Geological Survey here in Glacier National Park, the last of the park’s glaciers will be gone within 30 years. And that is an upper time limit. Talk to any ranger or visitor that has been here over even just the last ten years and you will hear personal stories of how different the glaciers in the park used to be. One naturalist I spoke with first started leading hikes to Grinnell Glacier 40 years ago and although she no longer leads others up there she still goes out each summer to see what’s become of it. You can hear the pain in peoples’ voices.
Today nearly every ranger, tour boat operator, or naturalist speaker, talks about how the climate is warming. They don’t force the issue with the public, but when the evidence is literally right in front of one’s nose (and early paintings, photos, and descriptions of the park’s glaciers are on display everywhere) the message is clear. The climate is changing.
I’ve given several talks here in the park over the last week. Unfortunately, the tourist season is pretty much over (the first snow of the season fell last night). They’d like me to come back next summer so I am going to try and work that out when I get back to the office next week. It’ll depend on what my budget looks like. I’ll then have ten days in Redlands before I head off to Acadia and Great Smoky Mountains National Parks to talk about the astronomical (and widely misunderstood) origins of tides and the seasons.
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