Aspen anomaly facts for kids

The Aspen anomaly is a special part of the Earth deep underground in Colorado, United States. It's like a 'soft spot' in the Earth's mantle (the layer below the Earth's crust) where earthquake waves travel slower. This soft spot is found right under the tallest parts of the Rocky Mountains.

What is the Aspen Anomaly?

The Aspen anomaly is an area deep inside the Earth's mantle where seismic waves (like sound waves from earthquakes) travel slower than usual. It's located beneath central Colorado, near the town of Aspen, Colorado. This unusual area seems to reach deep into the upper part of the mantle.

What Comes Out of the Ground?

Interestingly, a gas called Helium comes out of the ground above this anomaly. This helium has special features (called isotope ratios) that show it comes from deep inside the Earth's mantle.

How Does it Affect the Mountains and Rivers?

The Aspen anomaly is found under the highest parts of the Rocky Mountains, including areas like the San Juan Mountains and the Sawatch Range. Big rivers like the Arkansas River, Colorado River, and Gunnison River flow from this region and have carved out very deep canyons.

This whole area lifted up a lot about 5 to 10 million years ago, during a time called the Cenozoic Era. The Colorado River then carved away at the land. Even today, parts of the San Juan Mountains might still be lifting up because of the Aspen anomaly.

Some spots in rivers, like in Gore Canyon and Black Canyon, are called "knickpoints." These might show where the rivers cross the edge of the area above the anomaly. The Colorado River might even be affected by this anomaly all the way to Lees Ferry, Arizona.

Hot Springs and Volcanoes

You can find Hot springs and geysers (like mini-volcanoes that shoot hot water) above the Aspen anomaly. These release a lot of carbon dioxide gas and other gases. Some of these gases are food for special bacteria that live underground.

Volcanic activity from the Cenozoic Era is also linked to this anomaly. For example, a rock formation called the Twin Lakes pluton near Leadville, Colorado might be connected to it.

How Do Scientists See It?

Scientists use a method called seismic tomography to create images of the Earth's inside, similar to how doctors use X-rays. In these images, the Aspen anomaly looks like a tilted area where seismic waves are slow.

The Aspen anomaly is one of several "slow wave" areas under the western United States. However, unlike others like the Yellowstone hotspot, it doesn't have a large volcanic crater (called a caldera). Other geological features, such as the Colorado mineral belt and the Rio Grande Rift, might also be connected to the Aspen anomaly.

Where Did It Come From?

Scientists have different ideas about what caused the Aspen anomaly:

• Mantle Plume: It could be a mantle plume, which is like a hot column of rock rising from deep within the Earth. But its steep tilt is unusual for a typical plume.
• Melted Rock: It might be an area where rocks in the Lithosphere (the Earth's rigid outer layer) are melting. However, the lithosphere here might not be thick enough for this to happen.
• Ancient Structure: It could be a very old structure from the Proterozoic Eon, perhaps left over from a subduction zone (where one of Earth's plates slides under another). If this area had water trapped in it for a long time, it could have lowered the melting point of the rocks.
• Rising Asthenosphere: It might be caused by shallower hot rock rising from the Asthenosphere (the softer, flowing part of the upper mantle). This could be linked to processes where Earth's plates move or break apart.
• Weaknesses in the Crust: It could also be related to weak spots in the Earth's crust.