A Rare View of the Earth – Gros Morne National Park

We are now at Gros Morne National Park and we took a hike on the tablelands today. From a distance it’s a stunning landscape.

Up close it is almost entirely one kind of rock. It turns out that this is not your garden variety rock. This is peridotite, rock that makes up much of the earth’s upper mantle. The rock and soil that we normally walk on, dig in, even mine is all from the earth’s crust. We never see the mantle because it’s miles below the surface.

500 million years ago two tectonic plates of the earth’s crust pushed together here and the mantle rock, which is more dense than the crust, did not get pushed under like normal but ended up on the top of the crust. Eons of movement and erosion have left this bit of mantle exposed on the surface. And if you’re a geologist that’s a very big deal. It is such a big deal that this area is a UNESCO World Heritage Site.

This is peridotite, it has high levels of iron, magnesium, nickel, copper and chromium. If not exposed to the oxygen in the air the rock is very dark green, almost black. The orangey color is rust.

With pressure underground water can be forced into cracks in the peridotite and react chemically to make serpentinite. There were rocks like this scattered around.

Sometimes the serpentinite was an inclusion in the peridotite.

What adds to the strangeness of the landscape is that most plants can’t grow on peridotite. This is the Trout River Gulch. The land on the right is crustal rock and soil and supports a forest. The land on the left is peridotite; even though it has had the same timespan to erode and gets the same sun and rain, it is almost barren.

I learned that the strip of land the trail is on is the old roadbed. The growth along that is on the gravel brought in to build the road.

There are two other things to notice in this picture. The U shape of this valley is from glaciation, also very prevalent in the park.

If you can enlarge the picture and look closely at the farthest slope of peridotite, you can make out a line where the slope changes from brown mantle rock to the gray gabbro of the lower crust. If it had been a sunny day that might show up better. That is called the Mohorovicic Discontinuity. I didn’t even know I had captured that until I started looking for more information and came across a guided tour that I wish I had downloaded before the hike!

The information said even most lichen won’t grow on these rocks, but I found some that did.

I also found Moss Campion, which unfortunately was not in bloom.

Carnivorous plants also grow here. They don’t need to rely on the rocks for nutrients, they get minerals and nitrogen from insects they trap. There were pitcher plants all around.

I also found common butterwort, but not in bloom. They have sticky leaves that tiny insects get trapped on.

None of the park information mentions sundew, maybe because they are so small, but I found some. I love these tiny plants. Can you see the red spikes with sticky drops on the ends?

I also found white bog orchid, sometimes called boreal bog orchid.

There was so much to see, close and far. This is a view of Bonne Bay. It is a true fjord, a valley carved by glaciers and filled by the sea.

The trail ended at Winter House Brook canyon.

The brook came tumbling through the rocks there.

We also saw some travertine here. Calcium in the spring water that comes from the serpentization of peridotite is precipitating out as calcium carbonate, forming small patches of travertine. (Travertine is the fragile rock that forms the huge Mammoth Hot Springs in Yellowstone. Same thing here, but on a much smaller scale with no geothermal activity to accelerate the process.) Signs pointed out that the travertine is forming now, brand new rock, on rocks that are 500 million years old!

This wasn’t a very long hike, but it was full of wonders.