Geology Photo of the Week #36

The highlighted photo for this week comes from my last trip to New Zealand for the AMS12 conference a few years ago. They were taken at the end of a hiking trail in the Mount Cook area, it is behind the clouds looking straight ahead but you can kind of make out some small glaciers in the distance. However, the interesting stuff is all in the foreground.

These pictures highlight two really interesting phenomena. The first is the massive pile of gravel in the middle of the picture. It is called the Mueller Lateral Moraine and is a great example of a very recently formed glacial feature. Lateral moraines form as big gravel piles along the edges of a glacier, in this case, the Mueller Glacier, which has receded out of the picture.

The Mueller lateral moraine at the Mt. Cook glacier on New Zealand’s south island. (Photo: Matt Herod)

The second cool feature of this image is the water. At first glance, it may just look like muddy water, but there is more to it than that. If you look closer you can see there is some ridiculously blue water in the picture as well. The picture below shows it much more clearly.

Some cool blue water courtesy of rock flour. (Photo: Matt Herod)

Pretty cool looking water eh?! But, why is it so blue? The colour comes from a substance called rock flour. Rock flour is extremely fine grained sediment that is formed underneath a glacier by erosive action of basal sliding, freeze-thaw or meltwater erosion. The particles are so small that they don’t sink rapidly like a larger stone would, they stay suspended in the water column and change its colour from turquoise blue to milky white, all of which can be seen in this photo. One very interesting thing about this photo is the colour gradients that can be seen and the mixing of the blue stream with the milky pond. You can see the trailers of blue water entering and flowing into the pond and then gradually being diluted with the white water. Also, some little pools of water are super blue, while others are more pale, I imagine this has something to do with the amount of suspended sediment. I don’t really know, but it sure is interesting! Another strange thing is that I would have expected the streams to be white and the ponds to be blue. I am not sure why this inversion is taking place so if anyone has a suggestion I’d love to hear it! Maybe it has something to do with how cloudy it was, I’m not sure. Normally, in when rock flour laden stream enter a lake the lake is blue and the streams are white. Both colours are due to the suspended rock flour, but the colours are inverted here and I don’t know why….

The moraine and the mixing ponds (Photo: Matt Herod)

By the way, I am starting to run out of photos for this weekly series! I need to get out in the field more, but sadly I am trapped in the lab for most of this summer doing data collection. Therefore, if you have any photos you would like to see highlighted in the photo of the week let me know in the comments below, along with your email, and we can set something up. Otherwise, I’ll have to start posting pictures of plants soon!

Cheers,

Matt