- Where
- Gros Morne National Park
Newfoundland, Canada - Coordinates
- 49.4750° N
57.9500° W - Biome
- Serpentine barrens
- Rock age
- Thrust up c. 470 million yrs ago
- Status
- UNESCO World Heritage, 1987
- Best visited
- June–September
The short answer
The Tablelands are a flat-topped, rust-orange massif in Gros Morne National Park on the west coast of Newfoundland. The rock is peridotite — material from the Earth's upper mantle, normally found kilometres below the crust — pushed to the surface when the ancient Iapetus Ocean closed and continents collided roughly 470 million years ago. Gros Morne was inscribed by UNESCO in 1987 substantially because of it, and a 4-kilometre trail runs straight into the formation.
Why it's worth knowing
Two reasons, and the second is better than the first.
The first is that you are looking at the inside of the planet. Mantle rock does not belong on the surface. Here a slab of ocean lithosphere, instead of being subducted downward as it normally would be, was bulldozed up on top of the continent as the young Appalachians formed. The result is a complete slice of ancient sea floor — peridotite, gabbro, sheeted dykes and pillow basalt, an assemblage geologists call an ophiolite — sitting in the open air on a Canadian island.
The second is that this place helped prove plate tectonics. In the 1960s, when continental drift was still contested, the confusing rocks of western Newfoundland provided some of the field evidence that settled it. Geologists working here established that these rocks came from an ocean that had been destroyed. The Tablelands are not merely an illustration of the theory; they are part of the argument that made it.
The field notes
Why it's orange, and why nothing grows
Peridotite starts out dark greenish-black. Exposed to air and water it oxidises, and the iron in it rusts — which is why an entire mountain looks like the surface of somewhere else.
The barrenness has the same cause. Peridotite is very low in the nutrients plants need and very high in things they cannot tolerate, particularly nickel, chromium and magnesium. The result is a serpentine barren: not deforested, never forested. Cross the boundary and the vegetation stops in a line you can stand with one foot either side of.
The Moho, at ground level
The boundary between crust and mantle is called the Mohorovičić discontinuity, or Moho, and it normally lies 10 to 12 kilometres beneath your feet. A section of it is exposed here at walking height.
The mineral list reads like a geology exam: peridotite, serpentinite, dunite, pyroxenite, rich in olivine, chromite, nickel and cobalt. What matters for a visitor is simpler. Pick up a heavy rust-coloured stone on the Tablelands Trail and you are holding something that formed beneath an ocean floor that closed before there were trees.
A piece of peridotite. Heavier than it looks, rust-orange on the outside from oxidation, dark greenish-black where it has freshly broken. Every rock underfoot on the Tablelands Trail formed in the Earth's upper mantle. Put one in your hand and the interesting part is the weight — this is what the planet is made of, most of the way down.
Getting there
Gros Morne National Park is on the west coast of Newfoundland; Deer Lake has the nearest airport, about an hour and a half by road. The Tablelands sit at the southern end of the park, on Route 431 between Woody Point and Trout River.
The Tablelands Trail is an easy 4-kilometre there-and-back walk into Winterhouse Brook Gulch, and Parks Canada runs guided walks in season, which are worth taking — the landscape is much stranger once someone explains it. The Discovery Centre near Woody Point holds samples from the full ophiolite sequence. Summer, June through September, is the practical window.
Common questions
What are the Tablelands in Gros Morne?
The Tablelands are a flat-topped, rust-orange massif in Gros Morne National Park, Newfoundland, made of peridotite — rock from the Earth's upper mantle. It was thrust to the surface roughly 470 million years ago when the ancient Iapetus Ocean closed and continents collided, forming the Appalachians.
Can you really walk on the Earth's mantle at Gros Morne?
Yes. The Tablelands Trail is an easy 4-kilometre there-and-back walk directly onto exposed mantle peridotite. The formation also contains a section of the Mohorovicic discontinuity, the crust-mantle boundary that normally lies 10 to 12 kilometres underground.
Why are the Tablelands orange?
The Tablelands are orange because peridotite is rich in iron. The rock is dark greenish-black when fresh, but exposure to air and water oxidises the iron at the surface, effectively rusting the entire massif to a rust-orange colour.
Why do no plants grow on the Tablelands?
Peridotite is very low in the nutrients plants need and very high in metals they cannot tolerate, particularly nickel, chromium and magnesium. This produces a serpentine barren, where vegetation stops abruptly at the boundary of the rock rather than having been cleared.
How did the Tablelands help prove plate tectonics?
In the 1960s, when continental drift was still contested, geological fieldwork in western Newfoundland showed that the Tablelands rocks originated beneath an ocean that had since been destroyed by continental collision. That evidence contributed directly to establishing the modern theory of plate tectonics.
When did Gros Morne become a UNESCO World Heritage Site?
Gros Morne National Park was inscribed as a UNESCO World Heritage Site in 1987, recognised both for its exceptional natural beauty and for providing a rare example of continental drift in which deep ocean crust and Earth's mantle rocks are exposed at the surface.
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