Craters of the Moon
Craters of the Moon National Monument is the only National Park Service unit in Idaho that isn't a historic site. It is relatively isolated, but visitors will find an amazing wonderland created by some of the most powerful geologic forces on Earth. Before you read on, log in to BBLearn, go to Module 2, and select the Study Area. In the Study Area, go to Interactive Animations. Under Chapter 14, select the animation "Mantle Plumes (Hot Spot Volcano Tracks)." Use the animation to help you answer the following questions:
1) According to the animation, where do you usually find mantle plumes relative to plate boundaries?
2) How can you determine the speed of plate movement from hot spot-produced volcanoes?
3) What kinds of eruptions and what shape of volcanoes are normally associated with mantle plume hot spots?
The animation refers to the Hawaiian islands, easily the best-known example of a hot spot volcano chain in the world. The picture below shows not only the Hawaiian islands, but also the Hawaiian and Emperor Seamounts, which are chains of underwater, extinct volcanoes. A seamount used to be an island, but erosion and sea level rise eventually completely submerged it -- this will happen to every single island that comprises Hawaii someday (but not for many millions of years, probably long past when humans will still want to vacation there!).
1) According to the animation, where do you usually find mantle plumes relative to plate boundaries?
2) How can you determine the speed of plate movement from hot spot-produced volcanoes?
3) What kinds of eruptions and what shape of volcanoes are normally associated with mantle plume hot spots?
The animation refers to the Hawaiian islands, easily the best-known example of a hot spot volcano chain in the world. The picture below shows not only the Hawaiian islands, but also the Hawaiian and Emperor Seamounts, which are chains of underwater, extinct volcanoes. A seamount used to be an island, but erosion and sea level rise eventually completely submerged it -- this will happen to every single island that comprises Hawaii someday (but not for many millions of years, probably long past when humans will still want to vacation there!).
- Based on the line of seamounts and their ages (given in millions of years old, or Ma), what direction is the Pacific plate moving?
- Has it always moved in that direction, or has it turned slightly over the millenia? How can you tell?
Now that you understand how hot spots work in the ocean, let's take a closer look at the Yellowstone Hot Spot, and how it created Craters of the Moon and other basaltic landscapes in Idaho.
When the very first white Americans stumbled onto the Yellowstone Basin in the mid-19th century, they couldn't believe what they saw. Columns of superheated water shot high into the air at regular intervals. Pools of incredible color and equally deadly temperatures. Basins of bubbling, boiling mud. Vents of never-ending steam. Explorers called it "the place where hell bubbled up."
The Yellowstone hot spot is unique the world over for its amazing features, and the geologic process that underlies it is equally unique. While most hot spots occur far from plate boundaries, the Yellowstone mantle plume hot spot is only a few hundred miles from the Cascade subduction zone. Scientists aren't sure exactly why, but think it might be due to the age and position of the Juan de Fuca spreading center -- the "new" ocean floor basalt getting subducted under the North American plate is much wetter and warmer than older oceanic crust in most places. No matter how it happens, the hot spot under Yellowstone has been there nearly 20 million years, with the North American plate sliding right over the top of it.
The Yellowstone hot spot is unique the world over for its amazing features, and the geologic process that underlies it is equally unique. While most hot spots occur far from plate boundaries, the Yellowstone mantle plume hot spot is only a few hundred miles from the Cascade subduction zone. Scientists aren't sure exactly why, but think it might be due to the age and position of the Juan de Fuca spreading center -- the "new" ocean floor basalt getting subducted under the North American plate is much wetter and warmer than older oceanic crust in most places. No matter how it happens, the hot spot under Yellowstone has been there nearly 20 million years, with the North American plate sliding right over the top of it.
As the North American plate has moved westward over the hot spot, most of the time the continental crust is thick enough to prevent magma reaching the surface. But several times in the last 15 million years, magma has broken through to the surface, allowing lava to flow freely across the land. We still see evidence of these lava flows today across the Snake River Plain, and the largest flows are found in Craters of the Moon, which was over the top of the Yellowstone hot spot about 10 million years ago. The extent of the lava flows is easily seen in satellite images of southern Idaho (below).
Just like basalt lava flows in Hawaii and elsewhere, there are two types of lava visible at Craters of the Moon: the smooth, ribboned pahoehoe and the more crumbly, blocky a'a (can you tell these names came from Hawaii?). There are also cinders, caves where lava flowed through before it cooled, and lava "bombs" associated with some of the more explosive eruptions from the hot spot. Both in and between the lava flows, sagebrush and juniper islands thrive in the northern Great Basin climate of hot, dry summers, and cool, less dry winters. Because of all the black lava (with its low, sun-absorbing albedo), Craters of the Moon can see surface temperatures up to 170 degrees F in the summer!
Tens of thousands of people visit Hawaii each year to see the volcanic landscapes (since most never get to see actual lava). If you go to Craters of the Moon National Monument next time you are passing through southern Idaho, you'll see similar landscapes and save a bundle of money!