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Geologic Column
Big Lonesome Mountain
Lisa Rossbacher

“You’re probably not thinking about the rocks.” The opening statement came from the beginning of the orientation video at Gros Morne National Park in western Newfoundland, Canada. The park, however, is all about the rocks. Indeed, the entire island is known as “The Rock.” So how could anyone not be thinking about the rocks?

Visitors have struggled to find ways to adequately describe Gros Morne, which means “big lonesome mountain.” W.D. Wetherell wrote in The New York Times (July 27, 2003) that “Gros Morne is a place of reverent pilgrimage for geologists.” Wetherell went on to use his family’s descriptions of the park as “Yellowstone surrounded by an ocean” and “a maritime version of Yosemite.” The Moon Handbook to Atlantic Canada describes it as the “Galapagos of Geology,” a source for new understanding. Frommer’s Guide describes the area as “one of the world’s great geological celebrities.”

The park was named a UNESCO World Heritage Site in 1987 because of its geology, citing the following as reasons the area should be protected: “The park is internationally acclaimed for its complete portrayal of the geological events that took place when the ancient continental margin of North America was destroyed by plate movement, and represents an outstanding demonstration of glaciation in an island setting.”

Gros Morne shares an important characteristic with other “geological paradises” — the scenery can be understood at multiple levels while retaining its fascination.

For the casual visitor: A visitor, regardless of geological background, can appreciate the features in the park. To a novice, the park seems straightforward, impressive and understandable. Glacial features are everywhere and easy to identify: deep U-shaped valleys, hummocky moraines, small kettle lakes and scenic fjords.

The limestone breccia is a fascinating jumble of grey limestone chunks, with sizes ranging from less than a centimeter to multiple meters across.

The “Tablelands” dominate the horizon in the southern part of the park. The weathered surface rises more than 700 meters above the coastal road, with colors of pink, yellow, ochre and grey. Although a few plants have taken hold in crevices, the rock is mostly barren. Visitors seeing the Tablelands for the first time describe it as looking like the surface of the moon or Mars. No geologic background is required to see — and appreciate — this landscape.

What makes Gros Morne National Park so special is that its stories match the experience each visitor brings — or acquires while visiting. The more geology you know, the more you will see and the richer the visit will be, but the geology meets all visitors at their own level.

For the geologist: Geologists who have visited the west coast of Newfoundland get misty-eyed when they speak of Gros Morne. The landscape is straight out of a glacial geomorphology textbook.

The limestone breccias were generated by landslides that ripped up carbonates on the continental shelf and deposited them on the slope below.

The Tablelands are, as widely reported, the centerpiece of the park. They tell the story of the Iapetus Sea closing and subduction to the east, where oceanic crust was trapped, deformed and metamorphosed. As the ocean closed, ultramafic magma from the mantle rose and formed peridotite, dunite and gabbro about 500 million to 475 million years ago. The Tablelands are one of the few places on our planet where visitors can touch the crust-mantle boundary and stand on rocks that constituted the Mohorovicic Discontinuity during the Paleozoic Era (540 million to 250 million years ago). This transition zone is typically between 3 kilometers (for the thinnest ocean crust) and 75 kilometers (under continents) deep, so seeing these rocks exposed at Earth’s surface is a remarkable opportunity.

The Tablelands also illustrate a classic “ophiolite” rock sequence, with ultramafic rocks, intrusive and extrusive mafic rocks, sheeted dikes, pillow lavas and fine-grained ocean sediments. These are ocean crust and mantle rocks that were pushed up onto continental crust during the collision of tectonic plates. When I took a graduate seminar on ophilolites nearly 30 years ago, I never imagined I would see the full suite in front of me. “Awesome” is an understatement.

While the barrenness of the Tablelands is the most visible aspect to nongeologists, the lack of vegetation is a function of the peridotite and other mantle rocks that were pushed to Earth’s surface; the weathered rocks lack nutrients and have toxic levels of heavy metals.

And did I mention the trilobites? The brachiopods? The fossils represent both deep and shallow sea environments from the early Paleozoic.

I also can’t forget the moose. (Note: These are not fossils.) The major distraction from looking at and thinking about the rocks is the need, while driving, to to think about wildlife crossing the road — especially moose. This part of Newfoundland is “Moose Alley.” We saw three within about 30 minutes near the Tablelands. A close encounter can modify the front end of a vehicle in a flash. Watching for moose and other wildlife is an important part of driving on this island.

The best sites for teaching and learning geology are the ones, like Gros Morne, that build on whatever you know. A five-year-old can learn geology in this park, and so can career geoscientists.

Trust me. In this park, everyone is thinking about the rocks. Even the moose.

Rossbacher, a geologist, is president of the Southern Polytechnic State University in Marietta, Ga.

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