Geological History of Glacier National Park

Going to the Sun Mountain in Glacier National Park

Going to the Sun Mountain in Glacier National Park (Photo credit: Wikipedia)

Glacier National Park is home to one of the¬†worlds most classic¬†geological structures. The Lewis Over Thrust, discovered by geologists in 1901 dates back many millions of years. The Earths plates began to form the Rocky Mountains around 170 million years ago . . . . since then they have been eroded and reformed, but that’s the original story. During this time a major fracture was formed, tectonic forces pushing a huge rock wedge eastwards and upwards, cracking large volumes of older, softer sedimentary rocks, sending them plummeting down the wedge.¬†

So what makes the Lewis Over Thrust so remarkable? Well, I’ll tell you . . . it’s one of the few places on Earth where the overlaying rocks . . . i.e. the ones at the top . . . are much older than the underlying rocks . . . i.e. the ones underneath. The ones at the top are 1.4 billion years old, and the ones underneath are a mere 170 million years old.

The best way to get around Glacier National Park in the winter time is using snowshoes or cross country skis, both of which give you the perfect opportunity to get a close-up view of the many outcrops on show in the park. These sedimentary rocks really are some of the oldest in the world and still have many of their original characteristics – mud cracks, ripple marks and even impressions of raindrops. There are also some great examples of what you would expect from a landscape carved out by glaciers – cirques, horns, moraines and hanging valleys – some of the only remnants from millions of years of glacial formation followed by glacial retreat. In particular, take notice of;

  • Reynolds Mountain – a great example of a horn, a high, rocky, pyramid peak formed by glaciers as they carve out a mountain on three sides.
  • Mount Clements – another superb example of a horn, notice also the great pile of glacial debris at the foot of the mountain . . . a moraine.

To be honest, Glacier National Park is running out of glaciers, there is one as you hike to Grinnell Glacier, but some geologists fear that, if the current trends continue, there will be no more glaciers left in Glacier National Park by the year 2020 as teh result of global climate change. Ain’t that a shame!


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