My friend Jessica and I skipped out from the Geological Society of America meeting in Vancouver last weekend to go visit the Stawamus Chief –a gigantic granite monolith near the town of Squamish. What a lovely place –and what a great respite from the craziness of a big meeting in a big city!
I don’t want to repeat myself too much, because I wrote about this in an earlier post–but just the fact that granite is exposed at the surface requires deep time –inconceivably great lengths of time. That’s because granite forms from a molten state by slow cooling and crystallizing far beneath Earth’s surface –10 km or more usually –and THAT means the rock had to get uplifted and exposed at Earth’s surface through processes that we humans perceive as time-consuming–on the order of millions of years. Additionally, all the rock that used to be above the granite had to get eroded away in the process.
And Shannon Falls is right there too–Amazing! It sprays about 1000′ down a series of cliffs–and allows a good, up-close look at the granite. It’s actually granodiorite –which is a lot like granite except that it contains a lot more plagioclase, as opposed to alkali, feldspar.
So… the granite speaks to great amounts of time… and the waterfall–it speaks to the changing landscape. It falls down scoured and smoothed cliffs because the whole area has been shaped by glacial erosion. Not long ago, this area was under ice! (Longer though, than the beginning of planet Earth according to the Young Earthers). You can see some wonderful glacial polish and striations on fluted granite along the highway between the Chief and the town of Squamish.
click here for some more photos of intrusive igneous rocks.