Time and Three Cities
History - World Released - Jun 07, 2015
You’re walking in Central Park. The rock formations look polished; they are, from the last Ice Age. The glacier that covered Manhattan and all of the Northeast was a mile thick . As the glacier receded it polished the rocks with a jeweler’s precision. The rocks in Central Park are the hardest found on Earth. Geologists have determined that the world’s tallest mountain range ever (averaging 30,000 feet in height) once stood where you’re standing now, compressing these very rocks to their present density and hardness. You look around and wonder: what became of the mountains? They went the way of all ancient mountains: they wore away. The mountain range that once covered Northeast America was formed 450-million years ago by the collision of three continents. As the continents drew apart (and created the Atlantic Ocean), the mountains gradually wore down to what you see today. Whatever remained of them 50,000 years ago, the last Ice Age leveled.
Los Angeles was once an island off the coast of Mexico. The West Coast of the United States, beginning with the Baja Peninsula of Lower California, up through San Diego, Los Angeles, Big Sur, and ending just south of San Francisco, comprise a land mass known as the San Andreas Block. It was assembled from a number of islands about 30 million years ago which collided with the North American continent. This land mass is shaped like a surf board, which is appropriate for a coastline known for surfing. Riding atop the Pacific Plate, the San Andreas Block has been “surfing” north ever since. The Pacific Plate, on which the San Andreas Block sits, is gradually sliding past the North America Plate. People who live on the western edge of the North American Plate, such as my California friends in Palmdale, watch the San Andreas Block drift past their doors at the rate of about 1.5 inches per year. Or so it would seem.
Some thirty-miles beneath the earth’s surface, the two plates slide past each other at 1.5 inches per year, but not so on the earth’s surface. Near the surface, the opposing masses of bedrock tend to bind and stick. The pressure grows and then all at once the opposing masses slip, making up lost ground (so to speak). The result is an earthquake. The last major earthquake on the San Andreas fault line was at the northern end, resulting in the San Francisco earthquake of 1906. Both land masses had a lot of catching up to do that day: slippage was as great as 21 feet. The quake before that was near the middle of the fault line, in a place called Tejon Pass, in 1857. The last major quake at the southern end was about 300 years ago. This is where the next major quake is expected to occur.
The San Andreas Block has traveled 300 miles north since colliding with the North American continent. In another 30-million years, Los Angeles and San Francisco will intersect. We won’t be around to see it, so we’ll have to take geologists’ word for it.
Finally, there’s Chicago. A sea once covered what is now Chicago and most of central United States. When super-continent Pangaea began rifting apart 200-millions years ago, the forces on the North America continent created an uprise in land mass. The center of the continent gradually rose above sea level, the ocean drained away and the Great Plains emerged. Chicago wasn’t out of the water yet, however. The last Ice Age, which created Lake Michigan and the Great Lakes, left Chicago at the bottom of a lake geologists call Lake Chicago. Lake water did not flow east toward Niagara Falls and to the Atlantic, as it does now, but south, down the Illinois River to the Mississippi and to the Gulf of Mexico Eventually, the water level of Lake Michigan dropped and Lake Chicago dried up. The clay soil on which the City of Chicago and outlying suburbs now stand (and is so difficult for farmers and home owners to deal with) is the lakebed of Lake Chicago. When the City of Chicago became a thriving metropolis, sewage water and what to do with it became a major problem. Rather than continue polluting the waters of Lake Michigan (the city’s water supply), the Army Corp of Engineers did the seemingly impossible—reversing the flow of the Chicago River. Instead of letting it feed into Lake Michigan, they dug a canal south out of the city to connect the southern branch of the Chicago River with the Illinois River, thereby shifting the water flow to the Illinois River and down to the Mississippi to the Gulf of Mexico. This was good for Chicago, but bad for people who relied on the river for drinking water, such as Joliet, Peoria, and St. Louis. To address the problem, water reclamation plants sprung up outside Chicago that cleansed sewage water prior to release into the Chicago River.
At it turned out, this was still not enough. Whenever rain storms hit the city, the river flooded, water backed up, and sewage again polluted Lake Michigan. What to do? Go underground: dig out vast water holding tanks in the bedrock beneath the city. Known as the TARP project (“Tunnel And Reservoir Plan”), as of 2010 some 110 miles of subterranean caverns have been excavated, consisting of “deep tunnels, drop shafts, near-surface connection and control structures and dewatering pump stations.” Water overflow from storms is collected here and, after the emergency has passed, pumped back into the Chicago River. TARP began decades ago and the dig continues still.