New Zealand on Ice

Gary Hart Photography: Glacial Flow, Tasman River, New Zealand

Glacial Flow, Tasman River, New Zealand
Sony 24-105 f/4 G
1 1/3 second
F/16
ISO 50

One summer when I was a kid my family took a camping vacation to the Canadian Rockies. Bits and pieces of that trip return to me as vague memories, but one memory permanently etched in my brain is the color of Lake Louise and Moraine Lake. My dad, a very passionate amateur photographer, was frothing with excitement and must have gone through half his film budget (remember those days?) at Moraine Lake alone. Nevertheless, and despite my dad’s pictures, I couldn’t fully process a world where water could be that color and for many years after that doubted my memory.

Long before visiting New Zealand I accepted that water really can be that color, but still had few opportunities to view it. Then I started visiting New Zealand, where photographing the lakes and rivers gives me a little déjà vu—it’s just plain disorienting to see water this color.

So what’s going on?

In areas of persistent cold, snow can accumulate faster than it melts. Over many years of accumulating, the snow’s weight compresses it into ice and a glacier is born. A glacier is incredibly heavy; since pressure decreases the freezing point of ice, at the interface between the glacier and the underlying rock (where the pressure of the ice’s weight is greatest), melting ice lubricates the glacier and allows it to move downhill. The glacier’s extreme weight combined with this forward motion breaks up the rock. Embedded with these rock fragments, the glacier behaves like sandpaper, grinding the rock on which it slides into finer and finer particles. The finest of these particles is called “glacial flour.”

Meltwater from the glacier flows downhill, carrying scoured rock with it. While the larger rock particles simply sink, the glacial flour remains suspended in the runoff. While most of the sunlight striking water infused with glacial flour is absorbed by the suspended particles, the green and blue wavelengths aren’t absorbed; instead they scatter back to our eyes and we are treated to turquoise water. The water’s exact hue (whether it appears more green or blue) is determined by the size of the suspended particles, which dictates the relative amount of green and blue wavelengths they scatter.

About this image

The Hooker Valley track is a spectacular 3-mile hike beneath Mt. Cook to Hooker Lake. This gradually sloped trail follows the Hooker River’s twisting turquoise ribbon, snaking back and forth across the water on three swinging suspension bridges. It doesn’t take too much time on the trail to understand why this is one of the most popular hikes in New Zealand.

This year’s workshop group didn’t have time to do the entire 6-mile roundtrip, but since the beauty starts pretty much in the first 100 yards and doesn’t let up, we guided them up the track with instructions to take their time and photograph without concern for how far they got. It turns out most only made it to the first bridge, initially stopped by the view of the river and mountains, and then by the sunset that colored the clouds above the peaks.

This image came from fairly early in our bridge shoot, when clouds capped the scene and I took advantage of the soft light to stretch my exposure and smooth the water. Here I was a few yards up the trail from the bridge, which allowed me to make the river a diagonal stripe across the frame. Less than thrilled with the fairly boring foreground shrubs, I moved around a bit until I found a large rock to occupy the that part of the frame.