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Crater Lake: Why So Blue?

Crater Lake: Why So Blue?
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Oregon’s Crater Lake’s vibrant blue color knocks your socks off when you first look at it. All the pictures show it, but when you step out of the car to peak at it before heading on the trail or getting a piece of pie in the lodge, you realize it’s real. The photos weren’t doctored. It wasn’t just a marketing ploy.

So I decided to look into it. Why is the lake so blue, especially when its connecting streams are not? Fortunately, the United States Geological Survey in partnership with the National Park Service already examined the issue and published it (e.g. Larson, et al. 2003). The reference is at the base (with a hyperlink to the fact sheet), but here is a synopsis with photographs.

Crater Lake

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Blue Crater Lake Surrounds Wizard Island by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.The blue waters of Crater Lake surround Wizard Island. Photo taken from one of many viewpoints at the crater's edge. The blue waters of Crater Lake surround Wizard Island. Photo taken from one of many viewpoints at the crater’s edge.

Synopsis: an Update

On May 1, 2013, Linhai Li, a research assistant at Scripps Institution of Oceanography, wrote this great synopsis in the Linkedin comments section of this post, “For deep and clear crater lakes (or any deep and clear water), it is suppose to be blue, because water absorbs all light from orange to red, blue is the primary portion of light that can leave the water and reach our eyes. If you add some stuff into the water, the color could become green (by adding phytoplankton), brownish or redish (by adding dissolve organic matter), etc. However, if the water is shallow enough, it always look like the color of the bottom material.” A couple of Li’s specialties are ocean optics and ocean color, according to her profile. This nicely sums up the process. Keep it in mind as you look at the photographic description below.

Clear Annie Creek

The streams flowing from the lake are not blue. They are clear. Upon first glance, they look brownish, but that is actually just the rocks and sand on the creeks’ bed. The water is like glass, completely transparent.

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Clear Annie Creek by Shari is licensed under a Creative Commons Attribution 3.0 Unported License.Annie Creek flows from Crater Lake's vibrant blue waters. However, it is clear. Turns out, so is Crater Lake. The lake's blue color has to do with light and depth. Annie Creek flows from Crater Lake’s vibrant blue waters. However, it is clear. Turns out, so is Crater Lake. The lake’s blue color has to do with light and depth.

So why is Crater Lake blue?

Crater Lake is clear as well. But it’s a deep lake, deepest in North America, seventh deepest in the world: 1,949 feet (or 594 meters) at it’s maximum. Blue light from sunlight penetrates the water deeply. Water molecules scatter the light, and the blue color reflects back to our eyes. The blueness is most intense where particles and algae are low, since they would upset the water molecules bouncing the light off each other (Larson, et al. 2003).

Deep Blue Where Crater Lake is Clearest

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Deep Blue Crater Lake by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.The water has been clear as deep as 142 feet within the last two decades (before 2003). In August, it averages 90 feet. Clarity depends upon the absence of transported sediment and algae, which shifts. Crater Lake measured the clearest of all examined natural water bodies in the world (Larson et al. 2003). The water has been clear as deep as 142 feet within the last two decades (before 2003). In August, it averages 90 feet. Clarity depends upon the absence of transported sediment and algae, which shifts. Crater Lake measured the clearest of all examined natural water bodies in the world (Larson et al. 2003).

Lots of Sunlight Accessible to Crater Lake

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Mount Mazama from South by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported LicenseCrater Lake is actually the caldera of Mount Mazama in Oregon's Cascades. A massive eruption blew the mountain's top off about 7,700 years ago. Over several hundred years, water gradually filled the enormous hole about halfway. This photo looks at Mount Mazama from the south. Sunlight has ample opportunity to access the caldera's water: Crater Lake. This sunlight reaches great depths due to the water clarity (Larson et al. 2003). Crater Lake is actually the caldera of Mount Mazama in Oregon’s Cascades. A massive eruption blew the mountain’s top off about 7,700 years ago. Over several hundred years, water gradually filled the enormous hole about halfway. This photo looks at Mount Mazama from the south. Sunlight has ample opportunity to access the caldera’s water: Crater Lake. This sunlight reaches great depths due to the water clarity (Larson et al. 2003).

Plankton and Other Life in Crater Lake’s Depths

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Wind Blows over Crater Lake by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported LicenseWhile Crater Lake is clear, life does thrive within it. Because of the great light penetration, plant plankton grows at astonishing depths. The maximum amount of photosynthesis occurs between 131 and 262 feet (40 to 80 meters). Some forms of plant and animal plankton live at 600 feet (200 meters). Rainbow trout and kokanee salmon, both introduced to the lake decades ago, live within it: the trout near the shore, but the salmon mostly at 450 feet (150 meters [Larson et al. 2003]). While Crater Lake is clear, life does thrive within it. Because of the great light penetration, plant plankton grows at astonishing depths. The maximum amount of photosynthesis occurs between 131 and 262 feet (40 to 80 meters). Some forms of plant and animal plankton live at 600 feet (200 meters). Rainbow trout and kokanee salmon, both introduced to the lake decades ago, live within it: the trout near the shore, but the salmon mostly at 450 feet (150 meters [Larson et al. 2003]).

Links to Crater Lake & Mount Mazama Geologic History

  • Mount Mazama to Crater Lake
  • Annie Creek, Crater Lake: Columnar Scoria Preceded Volcanic Collapse
  • Links to Oregon Volcanic History

  • Oregon’s High Lava Plains
  • Twists of the 6,000-Year-Old Lava Forest, Oregon
  • Peek into Blue Basin, John Day
  • Reference

    Larson, Gary, Mark Buktenica, and Robert Collier
    2003 Deep Blue (Fact sheet about Crater Lake’s blue color produced March 2003 and designed by John Ledges). U.S. Geological Survey and National Park Service Partnership in Monitoring: USGS-FS-018-03. Electronic document, http://fresc.usgs.gov/products/fs/fs-018-03.pdf, accessed April 29, 2013.

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    Crater Lake: Why So Blue? by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.


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