Researchers model Earth’s crust, geology

by David Hyland

Tucked away at a lab beside the Mississippi River near St. Anthony Main, University researchers are building a 40-foot-long basin to visualize the sections of the Earth’s crust.
Dubbed the “Jurassic Tank,” the experimental basin is the first in the world to use a “sinking floor,” which enables researchers to reproduce geologic effects and events that have occurred throughout Earth’s history.
Geology professor Chris Paola said the tank will greatly enhance understanding about the Earth’s crust and the movement of tectonic plates, which are segments of the crust.
“I’m fascinated by the processes by which the history of the Earth is recorded,” Paola said. “If you can reproduce the way a recording’ is made, you can read it better.”
The tank will be used to simulate the subsidence, or sinking, of the Earth’s crust along with other geological events. Because the sinking is not uniform, it is often difficult to copy. The difficulty arises from the different forces that occur during sinking, thus creating a complicated pattern in the crust.
Researchers at the St. Anthony Falls Hydraulic Lab, where the tank is housed, believe its subsiding floor solves this problem.
The tank, which is 40 feet long, 20 feet wide and 5 feet high, resembles a large garbage dumpster. It has an open basin with the floor made up of 432 sheet metal honeycombs. On top of the honeycombs, researchers will place gravel and a rubber membrane.
The membrane represents the upper portion of the tectonic plate, and the underlying gravel represents the lower portions of the crust.
When completed later this month, the tank will be able to hold approximately 4,000 cubic feet of gravel with a total weight of 750,000 pounds.
Attached underneath each honeycomb is a cone connected to tubes. Using grain elevator technology, researchers will extract certain amounts of gravel by shooting a pulse of water into the bend of the elbow-shaped tubes. The water will push the gravel below the bend further down the tube, which allows the gravel above the bend to move down and the surface area to sink.
Sensors placed in the gravel will tell researchers what the elevation of the surface above that honeycomb is.
“It’s rather low-tech,” Paola said. “The mechanics of the basin are all made from parts you can buy at Home Depot.”
In the future, researchers hope to add a wave-maker to the tank to simulate the events on coastlines.
“What makes this facility unique is that we have control of the shape of the tectonic plate; we can generate any contour of the tectonic plate,” said Chris Ellis, one of the tank’s designers.
Paola said the size of the tank is another asset. Similar to a toy model, the larger the object, the more detail there is available, he said.
As a result, the subsiding floor can simulate a variety of area types. Paola said that researchers may visualize in part everything from the Himalayan basin in India where the Ganges and Indus rivers meet to the continental margin in the Atlantic Ocean.
At first, however, Paola said the researchers would study areas in which they could draw general principles of how the movement occurs. Once researchers learn more about how and why certain effects are produced, they can move to more localized situations.
The project began in 1993 when the researchers received grants to finance the construction of the tank. The tank eventually will cost almost $500,000. But before building the full size tank, researchers built a prototype two years ago. Though the prototype was smaller, its honeycombs were the same size so researchers could test the floor mechanism.
In addition to answering geologic questions, researchers said the tank may help detect the location of resources like oil, mineral or water deposits.
William Seyfried, head of the Department of Geology and Geophysics, said oil companies like Exxon and Mobil may send representatives to the tank in the future to better understand oil exploration.
“It represents one of those situations where you have an excellent opportunity to do basic science,” Seyfried said. “And then also do something that has important applications to industrial needs.”