The Continental Divide is the point in North America that separates the waters that flow into the Atlantic Ocean from the waters that run into the Pacific Ocean. To the west of the divide, all the rivers flow west, and on the other side all the rivers flow east. The Divide runs through Montana, Idaho, Wyoming, Colorado, and New Mexico. The path of the Rocky Mountains roughly traces out the divide. The Rockies began forming millions of years ago when the United States plate collided with the Pacific plate.

The United States plate and the Pacific plates are two of about a dozen plates that slowly float around the Earth's surface in an underground region known as the Lithosphere. The Lithosphere is moved around by a sea of molten rock beneath Earth's surface known as the Asthenosphere. When two plates collide underground, they produce mountains in a giant slow motion collision. This is dramatically displayed in South Asia where India is slowly mashing into China, producing the Himalayan mountains. This sort of collision is also going on beneath the United States.

You cannot see what goes on below the surface of the Earth, but you can see what happens on the surface. In the heart of the Continental Divide in Yellowstone National Park, there is a whole lot of geological activity. Yellowstone was the world's first national park. President Ulysses S. Grant established the park in 1872. The name Yellowstone is thought to come from a translation of the Native American Minnetaree word mi tsi a-da-zi, for the yellow cliffs along the Yellowstone River.¹

What makes Yellowstone special is a giant hotspot of magma (melted rock) that reaches up from the Earth's center to within a couple miles of Yellowstone's surface. What would normally be underground lakes have become boiling kettles of water erupting out of the ground like a champagne cork. The superheated underground lakes form hot springs, mud pots, fumaroles, and my favorite, the geyser.

Hot springs are basically a natural hot tub. Although you would not want to take a dip in some of these, because they can get as hot as 140 degrees! Hot springs have beautiful colors because of the different chemicals and life forms that live in them. The yellow color is formed from sulfur dioxide which makes hot springs smell like rotten eggs. Hues of red come from iron oxide, the same stuff that forms rust. Hot springs become pink, orange, brown, and green from different bacteria and algae that live in the hot water.

Mud pots are hot springs that do not have enough water to overflow their pool, so the water just stays there boiling away at the rocks surrounding it. Acid within the water works to break down the surrounding minerals from the rocks and all those minerals get mixed into the water to form goopy mud.

Geysers are the most exciting geothermal activity to watch at Yellowstone. The Old Faithful geyser is the most famous because it is the most predictable. Every 79 minutes or so it sends a column of water 184 feet into the air for up to five minutes, letting out 10,000 gallons of water! There are bigger geysers in the park, but none as frequent as Old Faithful, which makes it very popular with the tourists.

Fumaroles are weak geysers that do not have the right plumbing to shoot out streams of water. Instead they vent steam, sometimes letting out a roar.

The Park is home to many different kinds of animals, including grizzly bears, moose, and grey wolves. You can also see the only wild bison herd on the planet. All these animals live in an area where pools of boiling water, mud, and acid make a walk in the fields a dangerous trip.

The bison have an interesting story. (By the way folks, bison and buffalo are the same animal, they just go by two names). The bison crossed over the Bering Strait up in Alaska over ten thousand years ago. It is thought that the first Americans followed the bison because they hunted them for survival.

The bison thrived in the North American plains. At one point there were over thirty million bison! When European frontiersmen decided that bison were an unwanted neighbor (they had the annoying habit of knocking down trains in giant herds), it was a not a fun time to be a bison. They were slaughtered by the millions and almost completely wiped out. Before the government took action, the number of bison was down to less than one thousand. Today, they have been successfully protected and there are about 200,000 in the United States. The ones in Yellowstone are the only free herd in the United States; all other bison live on ranches and some are even turned into buffalo jerky and buffalo burgers. Yum!

Teddy

Please email me at: teddy@ustrek.org