The Grand Canyon, cathedral of time, is losing its river – 06/15/2023 – Environment

Down below, beneath tourist inns and shops selling key chains and incense, past intermittent windswept creeks and brown valleys dotted with agave, juniper and sagebrush, the rocks of the Grand Canyon seem timeless. The oldest date back to 1.8 billion years ago—not just eternities before humans first laid eyes on them, but eternities before evolution endowed any organism on this planet with eyes.

Spend enough time in the canyon and you might start to feel a little out of time yourself. The immense walls form a kind of cocoon that protects you from the modern world, with its cell phone signal, its light pollution and its disappointments. They always draw your gaze upwards, as in a cathedral.

You might think you’re seeing all the way to the top of the canyon. But further up and down are more walls, and above them even more, out of sight except for an occasional glimpse. That’s because the canyon isn’t just deep. It’s wide, too: 18 miles across at its widest point. It is no mere stone cathedral. It’s a veritable realm: huge, self-contained, an alternate reality that exists majestically outside our own.

But the Grand Canyon remains tethered to the present at one key point. The Colorado River, whose wild energy carved the canyon over millions of years, is in turmoil.

As the planet warms, there is less snow, and the lack of snow is starving river sources in the Rocky Mountains of water, while higher temperatures rob them of more water through evaporation. The seven states served by the river are using every drop of water it can supply, and while a wet winter and a recent agreement between the states have staved off the river’s collapse for now, its long-term health remains in deep doubt.

The Colorado flows so far beneath the rims of the Grand Canyon that many of the 4 million people who visit the national park each year see it as just a wisp, shimmering in the distance. But the fate of the river has profound importance for the 450km-long canyon and how future generations will experience it. Our subjugation of the Colorado River has already triggered far-reaching changes in the canyon’s ecosystems and landscapes. These are changes that a group of scientists and graduate students at the University of California, Davis set out to see firsthand, traveling in inflatable boats: a slow journey through deep time, at a time when the Earth’s clock seems to be speeding up. .

John Weisheit, one of the leaders of the conservation group Living Rivers, has been rafting across Colorado for four decades. He said seeing how much the canyon has changed in his lifetime makes him “hugely depressed. You know how you feel when you go to the cemetery? That’s how I feel.”

Even so, he continues to go to the canyon every year or so. “Because we need to see an old friend again.”

Ages and times immemorial ago, this place was a tropical sea, with snail-like beings that had tentacles tracking their prey beneath the waves. After that it turned into a vast sandy desert. Later it became a sea again.

At some point, energy from deep within the Earth began to push a large section of Earth’s crust skyward and into the path of ancient rivers that crisscrossed the land. Over tens of millions of years, the crust was pushed upwards and rivers flowed downwards, sculpting the landscape with their ups and downs. An abyss opened, which the meandering water united over time with other canyons, forming a single one. Weather conditions, gravity and tectonic plate movements have distorted and sculpted the surrounding exposed layers of stone, creating fluid and fantastic shapes.

The Grand Canyon is a planetary spectacle like no other—and one that happens to be home to a river that 40 million people depend on for their water and energy supply. And the event that crystallized this strange, uneasy duality—one that changed almost everything for the canyon—seems almost small compared to all the geological turmoil that went before it: the construction of a concrete wall 15 miles upstream.

Since 1963 the Glen Canyon Dam has dammed the Colorado River for nearly 200 miles in the form of America’s second largest reservoir, Lake Powell. Engineers constantly assess water and electrical needs to decide how much of the river’s water to let through the dam and out the other end, first to the Grand Canyon, then to Lake Mead, and finally to the fields and homes of Arizona, California, Nevada and Mexico.

The dam processes Colorado’s uneven flows — which can be a trickle one year and a violent runoff the next — into something less extreme at both ends. For the canyon, however, river regulation has brought heavy environmental costs. And as water continues to decline due to drought and overconsumption, those costs could rise.

A few months ago the water level in Lake Powell was so low that there was barely enough water to turn the dam’s turbines. If it drops below that level in the next few years —and everything indicates that it could happen—, electricity generation will be paralyzed, and the only way in which water will leave the dam will be through four pipes located closer to the bottom of the lake. As the reservoir level drops further, the pressure pushing water through these pipes may decrease, so that smaller and smaller volumes will come out the other end.

If the water level dropped much lower than that, the pipes would start sucking in air, and in time Lake Powell would become a “dead pond”: not a drop of water would pass through the dam until the water reached the tops again. pipes.

With these doubts about the future of the Colorado River in mind, UC David scientists inflated blue dinghies on a cool spring morning. At mile zero of the Grand Canyon, the river’s flow is about 2,134 cubic meters per second, rising towards 2,743 — not the lowest flow on record, but far from the highest.

The big problem with low water in the canyon, the one that exacerbates all the others, is that things stop moving. The Colorado River is a kind of circulatory system. Its flow has carved the canyon, but also sustains it, making it suitable for plants, fauna and humans who travel through it in boats. To understand what has happened since the dam began to regulate the river, let’s first consider the smaller things that the water displaces or fails to displace.

On its descent from the Rockies, the Colorado River accumulates immense amounts of sand and silt, but the dam basically prevents all of this from flowing into the Grand Canyon. Downstream tributaries, including the Paria and the Little Colorado, add some sediment to the Colorado, but far less than is retained in Lake Powell. And when the water flow is weak, more sediment ends up being deposited in the river bed.

As a result, the canyon’s sandy beaches, where animals live and people who hike the river camp at night, are shrinking. Beaches that once were the width of major highways are now more like two-lane highways. Others shrank even further.

In addition to sand, the river is no longer carrying larger objects into the canyon. Small and large stones periodically fall into the river from hundreds of tributaries and secondary canyons, often during floods, creating bends and rapids in the river. With less strong water flows to carry this material, more of it is piling up in those bends and rapids. As a result, many rapids became steeper, and the paths on which boatmen navigated them narrowed.

It’s the sixth night for the scientists at UC David in Colorado, and the graduate students are sitting in camp chairs, reflecting on what they’ve seen.

They are preparing for careers as academics, experts, and policy makers—people who will help determine how we live with the environmental consequences of past choices. Choices such as damming rivers.

Yara Pasner, a doctoral candidate in hydrology, says that she feels a duty to reduce the burden on future generations, even because – or perhaps simply because – our ancestors did not pay us that courtesy. “There was the mentality that ‘we screwed things up and the next generation will have more tools to fix it’.” Instead, she commented, we find that the consequences of many past decisions are more difficult to deal with than previously thought.

^{Translated by Clara Allain}