Interior View: Weinberg College - Northwestern University

Interior View

Patricia in the Yucatan

Patricia Beddows leaves little to chance when she and her team pack for the study trip she leads to Mexico’s Yucatán Peninsula each spring. Beddows, an assistant professor of instruction in earth and planetary sciences, typically stuffs about 600 pounds of gear into 12 suitcases. She’ll need all of it as she leads a dozen students through the Yucatán, where the earth readily yields clues to the changes wrought by time.

Over 10 days, the group journeys across the area to discover how the landscape has evolved over millennia. Their first stop is the actively growing Meso-American barrier reef, the second longest in the world. They then visit a lagoon, a beach face and a modern beach ridge before heading inland to explore progressively older features.

Together they study quarries, where ancient reefs and beaches are again exposed to the sun, and jungle-water pools where the bedrock has collapsed into underground caves.

“It’s a very tactile, visceral and immersive experience that goes well beyond their textbooks,” says Beddows.

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Exploring an explorer’s backpack

Caves are an essential part of the geology of the Yucatán. Wearing protective headgear, Beddows and her students spend ample time exploring them.

“Cave systems are massive underground rivers,” Beddows says. “What we’re first interested in is the physical structure: how did they form, where is the water coming from, where is it going to?” Using measuring tape, Beddows and her students survey these subterranean waterways to see if they might have formed when the sea level was at a particular height.

Each day, Beddows uses a whiteboard to sketch out geological processes. The boards eliminate the need for paper in the water-soaked Yucatán and allow Beddows to illustrate phenomena such as the movement of water through lakes and channels to the final discharge into the Caribbean Sea.

Using these tools, Beddows and her students triangulate their way through the caves. The compass (left) establishes the deviation from true north, while the clinometer (right) marks changes in elevation. Together, the instruments provide more evidence of the history and evolution of the area.

This sieve stack features a series of filters with progressively smaller holes, so that students can separate larger sediment from smaller, finer grains. “Then we weigh the amount of sediment that ended up on each of the different layers and graph that,” Beddows says. The exercise yields clues to the amount of energy within a system. Larger grains, for example, require more energy to move.

Beddows fills ping-pong balls with varying amounts of water to measure how fast a current is moving. Heavier balls float in salt-loaded, higher-density marine water. Lighter balls bob in bodies filled with more rainwater. “They literally let us see where the water is flowing,” Beddows says.

“We’re bashing rocks all the time,” Beddows says. “An exposed rock is usually weathered and covered with dirt and vegetation. We use the hammer to get at the fresh, raw rock that’s underneath.” The fossils and patterns in the rocks indicate the various environments, such as the lagoon or the beach, where the sediment was deposited.

Regular cameras don’t hold up very well in the wet and rainy Yucatán. In addition to being more durable, Beddows’ underwater camera features high-definition video, a GPS system and a microscope mode that enables on-site analysis of sediment samples.