Great Lakes Earth: The Americas

[Jdailey]

The Appalachian Range, at first glance, doesn’t seem so different—low-lying hills covered in forest dominating the eastern landscape. However, they are taller—9,930 feet above sea level at the highest, compared to Mount Mitchell back home, which is over 6500 feet above sea level. Indeed, the Appalachians on Great Lakes Earth are a labyrinth of solid gneiss and granite, a macrocosm of the Black Hills and Yosemite, both of which we have but Great Lakes Earth doesn’t.

The mountains of the American West have some major differences. For starters, only the Rockies stand firm—no Coast Range, no Grand Canyon and most certainly no Sierra Nevada. The Rockies on Great Lakes Earth have a different road from ours. If we use it on our map, we’d see the Rockies starting in the Canadian village of Chesterfield and meandering to the next point, Rapid City, South Dakota. Once there, it makes another meander through the eastern borders of Wyoming, Colorado and New Mexico before making one last meander across the Texas-Mexico border. While our Rockies stand no taller than 14,440 feet above sea level, the tallest peak in a Great Lakes Rockies is measured to be 14,505 feet. Back home, our Rockies formed between 80 and 55 million years ago through the Laramide Orogeny, the subduction of the North American and Pacific Plates at a shallow angle. Their Rockies first formed 80 million years ago as the result of a collision between eastern and western North America. They stopped becoming active as recently as 30 million years ago. The main rocks of the range are schist, granite and gneiss, tough rocks with small vulnerabilities.

Behind the Rockies, which could vary in width between 75 and 300 miles, stands a plateau varying in elevation above sea level between 3600 and 8,000 feet. It covers what we would recognize as mainland Nunavut, Northwest Territories, Saskatchewan and Alberta in Canada; Montana, Idaho, Utah, Nevada, Colorado, Wyoming, Arizona and New Mexico in the United States; and Chihuahua, Durango, Coahuila, Nuevo León, Tamaulipas, Aguascalientes, Guanajuato, Querétaro, San Luis Potosí and Zacatecas in Mexico. Encrusting the plateau at the top is an igneous province of basalt, 200,000 square miles in area, the result of lava flooding western North America from 57 to 40 million years ago.

It is up north, from British Columbia to Alaska, that the iconic peaks of the Cascades stand firm. What we’d recognize as the Alaska Range in southern Alaska is an extension of the Cascades, turning the over-20,000-foot Denali into America’s largest volcano.

True to the spirit of the planet’s name, North America is full of large lakes. The largest of which is Agassiz. To have an idea on the shape, size and scope of Agassiz, we must look at the familiar faces of the Great Lakes—Superior, Michigan, Huron, Erie and Ontario—and then flood off the entire basin. This is Lake Agassiz, 95,000 square miles and 1500 feet at its deepest. Agassiz started out as a few tectonic depressions that expired some 20 million years ago. They wouldn’t become one lake until the ice bulldozed the depressions during the Pleistocene glaciations.

There are great lakes west of the Rockies as well. In fact, they could be identical to the lakes that used to dot the American West during the Pleistocene back home. Lake Bonneville is the largest—20,000 square miles in area and more than 1,000 feet at the deepest. Following Bonneville is Lake Lahontan, 8500 square miles and only 150 feet deep.

Comparing Great Lakes Earth to ours, we’d find that all land below sea level has become water, and Death Valley, the continent’s lowest and hottest point, is no exception. In its place is Lake Manly, a long but narrow strip of water fed by rivers flowing from Bonneville. It stretches only 50 feet long but gets no deeper than 600 feet.

The Yellowstone mantle plume is still present. Except that instead of Wyoming’s northwestern corner, it can be found in northeastern California. The latest eruption was roughly 10,000 years ago and it wouldn’t awaken again for another 600,000 years. The plateau itself covers an area of 5,000 square miles and stands almost like an island between the surrounding lakes and lowlands.

Comparing their South America to ours, there’s not much difference to find. The Andes themselves, though equal in length and width to our own, are taller and more active—the highest currently stands 30,111½ feet above sea level (not 22,841, as was the case back home) and the annual average of volcanic eruptions measures in at 50 per century.



How would these changes affect the Americas’ climate, weather and landscape?

How would they affect the danger zone called Tornado Alley?

Will the Midwest still be prairie?

Will the Wild West still be desert?

Will the Southeast still be swamp and forest?

[waldronate]

The short answer to all of your "will the" questions is probably "yes". The southwest is desert primarily due to its latitudinal position and cold offshore current. The Southeast would still be humid because of the presence of the warm Gulf of Mexico and warm Gulf Stream that allow for high evaporation. The Midwest would still be prairie due to latitudinal position and distance from coastal influences. Tornado alley would probably still be there due to the seasonal high that's currently generated by the Colorado Plateau, but would be generated by the volcanic one in your concept.

Replacing the basin and range province with a relatively smooth area would have some effects, of which the most notable would be elimination of the vast pluvial lakes that you show in the last image (largely formed by melting of glaciers on now non-existent mountains). Those lakes are generally nestled between two mountain ranges formed (as some theories have it) by shallow subduction of a western coastal plate that bumped along the bottom of the eastern plate rather than diving deep. Like pushing a carpet over a rough floor, fairly regular rumples (the mountains) formed. The deep area of Death Valley probably wouldn't be there, meaning no Lake Manly.

The wild west is characterized by lots of mineral resources generated by the placement of the western ranges. If a relatively cold and solid plate were to take the place of areas west of the Rockies, then it's likely that those resources wouldn't be there. Certainly no California Gold rush, no Comstock Lode, no Cerro Gordo. There also wouldn't be the evaporate deposits that are important (e.g. the soda lakes like Searles Lake, CA or the borax deposits at Boron, CA) to global commerce. There wouldn't be life forms like the giant redwoods or bristlecone pines. There would likely be more prairie elements in the mid coast and the deserts might be a bit wetter without the mountains to squeeze out moisture.

[Jdailey]

"Tornado alley would probably still be there due to the seasonal high that's currently generated by the Colorado Plateau, but would be generated by the volcanic one in your concept." 1) So northeastern Nebraska will still be in the Alley? 2) What "volcanic one"?


Have you not read the lava fields "encrusting the top of the plateau", meaning it might not be as smooth as you think?


Try reading the maps as flatly as presented, not outside the context.

[waldronate]

You're quite right. My poor reading comprehension and assumptions led me to assume that the large igneous province that covers the top of your plateau was somehow of volcanic origin. Clearly the lava is non-volcanic. My apologies.

[Jdailey]

So northeastern Nebraska will still be in the Alley?


Tibet is not smooth. What makes you think this plateau will be?