Glacier Bay National Park, located in southeastern Alaska, is a pristine wilderness area renowned for its breathtaking landscapes and rich natural diversity. This UNESCO World Heritage Site encompasses over 3.3 million acres of fjords, glaciers, rainforests, and rugged coastlines. The park is home to a remarkable array of wildlife, including grizzly bears, bald eagles, humpback whales, and seals, making it a haven for nature enthusiasts and photographers. The highlight of Glacier Bay is its ever-changing glaciers, which calve massive icebergs into the bay, offering a dramatic display of the Earth's dynamic processes.
Glacial erosion is a fascinating natural process caused by the huge power and movement of glaciers. When glaciers move forward, they act like massive bulldozers, putting a lot of pressure on the rocks beneath them. This pressure, combined with the rough action of rocks embedded in the ice, slowly removes material from the land. One interesting thing about glaciers is something called "glacial flour." Glacial flour is made up of very tiny grains of sediment, like fine sand, that come from rocks being ground up beneath the glacier's heavy weight (abrasion). As glaciers move, they press on the rocks, causing them to break into smaller pieces. These pieces travel with the glacier, getting crushed into even smaller bits along the way. When you see water from melted glacier ice, it often looks milky and cloudy. That's because of the glacial flour in the water. This sediment-filled water is essential in wearing down and smoothing the landscape as it scrapes and rubs against rocks.
As you travel into Glacier Bay, one of the things that might catch your attention is the color of the water. The vibrant colors seen in glacial flour are the result of a fascinating chemical process. Glacial flour consists of extremely fine particles of rock that are suspended in water. These particles are so tiny that they scatter sunlight differently than larger particles or clear water. When sunlight, which is made up of various colors, passes through the water with glacial flour, it gets scattered in all directions. This scattering of light is called "Rayleigh scattering." Now, here's where the magic happens: shorter wavelengths of light, like blue and green, are scattered more than longer wavelengths, such as red and yellow. As a result, the blue and green colors are more strongly scattered in all directions, making the water appear milky and the colors more pronounced. The presence of glacial flour also absorbs some of the light, enhancing the intensity of these colors. So, when you see a glacial river or lake with that stunning milky turquoise or vibrant blue hue, it's not just the result of the suspended particles; it's also the fascinating interplay of physics and chemistry that makes the colors so strikingly beautiful.
One other topic worth mentioning is Stokes Law. Stokes' Law is a fundamental principle in fluid dynamics that helps explain the settling rate of particles, including glacial flour, in a fluid medium such as water. This law states that the settling velocity of a small particle in a viscous fluid is directly proportional to the square of the particle's radius, the difference in density between the particle and the fluid, and the acceleration due to gravity, while inversely proportional to the viscosity of the fluid and the distance over which the particle is falling. It might sounds complicated, but don't worry, you won't have to do any calculations! In the context of glacial flour, which consists of tiny sediment particles suspended in water, Stokes' Law plays a crucial role in determining how quickly these particles settle to the bottom of a body of water. Smaller glacial flour particles with smaller radii will settle more slowly than larger ones due to their reduced settling velocity.
Logging Requirements:
- As you travel into Glacier Bay, keep an eye on the appearance of the water. At what distance from the glaciers does glacial flour become visible within the water? You can use the posted coordinates as the measuring point, since it is near the centroid of where the glaciers are concentrated.
- Based on Stokes Law, and the distance from the glaciers at which you observed the glacial flour (question 1), what can you conclude about the particle sizes of the glacial flour?
- At the posted coordinates, describe the color of the water. What are the weather conditions? How do you think the color of the water is impacted by weather?
- Does the intensity of the water color change when you observe it directly from above compared to when you view it from a distance? Why do you think the color appears different?
- Upload a photo taken in the area. You do not need to be in the photo, though it is strongly encouraged.