The Earth Story

Double Rainbow Caldera This shot of double full rainbows was taken by Jasman Singh Mander after a storm and shared through the US Department of Interior’s feeds. The beginning of a rainbow occurs as sunlight enters a raindrop. As the light enters the water, the light slows down and is refracted, changing path to go towards the center of the bubble. However, not all refractions are the same. White light, as from the sun, contains all the colors mixed together, but when light bends, individual colors will separate, with violet light refracting the greatest and red light refracting the least. These rays of light then hit the far side of the water droplet and reflect back out of the front of the droplet, but in a slightly different direction from where they came in. Thus, the main rainbow comes from light being separated and reflected back, and it shows up when the sun, the water droplets, and your eyes form the correct angle.

Stratigralicious!

This is pretty awesome. The Great Lakes in North America are apparently a tough place to do stratigraphy. Geologists would love to be able to take cores through these lakes and say how the chemistry of those lakes changed over time, but using those lake records requires knowing how old the layers are. There is a lot of reworking of carbon in the sediments, preventing Carbon-14 dating from being used to date any specific layer, so scientists led by researchers at the Large Lakes Observatory at the University of Minnesota Duluth went looking for something else they could use to date an individual layer, and they found this.

The scientists pulled these tiny chips from a core near Isle Royale in Lake Superior. These shards of rock, seen zoomed in under an electron microscope, are igneous. You can see the sharp edges of broken bubbles, ruptured in a volcanic explosion. They analyzed the chemistry and found that these match the eruption products of the Mount Mazama blast 7600 years ago, the eruption that led to the formation of Crater Lake.

The Scientists now know that they can use the presence of these ash layers to date other sedimentary cores in the Great Lakes. Beyond that, here’s ash from a volcano on the other side of the continent dropped into the Great Lakes and still trapped there today, and I think that’s kinda cool!

-JBB

Image credit and original paper, Spano et al., 2017 http://bit.ly/2C7aIgt

Mountain with a Hole in the Top

The Cow Creek Band of Umpqua Tribe of Indians tells a tale from long ago about the animal-people and the man-people. This shortened version of the story was told by Ellen Crispen, a Cow Creek descendant, to historian W. K Peery.

A very long time ago, the animal-people and the man-people shared the same language. They lived in the shadow of a snow-capped mountain. The bear, deer, panther and elk shared the mountain area with the man-people, and they lived in peace. An evil chief arose among the man-people, and he believed he was greater than Old Man God. He turned the man-people against the animal-people. He ordered them to kill the animal-people. The chief of the animal-people sought the guidance of their god, Tamanous, who told them to flee. The wildcat remained behind because he wanted to become chief of the animal-people after Chief Bear left. Man-chief was told that all the animals had fled. He went ouside and saw wildcat. He decided he did not like wildcat, and picked him up and burned off his tail.

Tamanous was very angry that wildcat was hurt. Suddenly, he caused a great wind to blow from the top of the mountain. Trees fell, and man could not breathe the hot wind. Black smoke rolled over the mountain top. Fire came out of the top. The mountain flew into the air, and then landed down on the earth with a sound like thunder that shook everything. The mountain no longer had a top. The man-people were all dead. Over time, water filled the great hole in the top. Tamanous decided to put the souls of the man-people in the big water hole at the top of the mountain. The animal-people eventually returned, but they could no longer speak the same language as the man-people. Old man God told the man-people to never return to the hole on the top of the mountain.

This story is an example of geomythology. The story is an ancient explanation of the formation of Crater Lake caldera in south-central Oregon. Crater Lake, at a depth of 592 meters (1,943 feet) is the deepest lake in the US and ninth deepest in the world. The eruption of Mount Mazma that created the caldera occurred about 6,000 to 8,000 years ago, and stories of the event live on in ancient myths. Although myths like this one include metaphor and supernatural elements, they can still give us some insight to past geologic events. So, the next time you read or hear an ancient story, remember that the roots of that story may be based on eyewitness accounts of real geologic events of the past.

-Amy

References:

http://www.cowcreek.com/the-mountain-with-a-hole-on-top

http://www.craterlakeinstitute.com/online-library/klamath-indians-southern-oreogn/myths-crater-lake.htm

http://www.stanford.edu/dept/HPS/MayorGeomythology.pdf

Image credit Zainubrazvi, Wikimedia Commons

That is blue.

This is what these type of video clips were made fore. Look at that mirror reflection!

Beauty in Destruction: Crater Lake National Park

Crater Lake rests at the southern crest of the Cascade Mountain Range in southwestern Oregon. It is approximately 9.7 km (6.02 mi) in diameter between its widest points and 594 meters (1,949 ft) deep, making it the deepest lake in the United States and the 7th deepest in the world (though this number often fluctuates between seasons). This is interesting when taking into account that there are no inlets or outlets to or from the lake. All of the lake’s water is collected rain and snowfall from over the course of hundreds of years which gives Crater Lake some of the cleanest water in North America. To preserve this amazingly clean water, park services have kept Crater Lake extremely secluded with few roads leading to the lake area. Additionally, no private boats are allowed on the lake aside from those of regulated boat tours.

This little slice of heaven was not always so quiet and peaceful though. The lake was formed when an ancient volcano, Mount Mazama, erupted and collapsed around 7,500 years ago. Molten lava poured in and sealed the base of the caldera and then over hundreds of years, precipitation filled this void and created the lake that exists today. Following its main eruption, for hundreds of years several smaller eruptions created cinder cones on the base of the lake. Today, only one remains visible above the water, known as Wizard Island. Wizard Island’s summit stands 233 meters (764 ft) above the water level which offers good hiking and stunning scenic views.

Crater Lake is widely known for its deep blue water and its unique geology that tells that story of its violent past. While standing on the either the caldron’s edge, or from the summit of Wizard Island, it can be hard to believe that such beauty can stem from such a catastrophic event. This is a common pattern in nature and the most we can do is appreciate and preserve these gems that our planet has to offer.

-Pete D

Photo Credit: Tyson Fisher, National Geographic

References: 1. http://www.nps.gov/crla/index.htm 2. http://vulcan.wr.usgs.gov/Volcanoes/CraterLake/description_crater_lake.html 3. http://pubs.usgs.gov/fs/2002/fs092-02/ 4. http://www.craterlakeinstitute.com/online-library/nature-notes/vol7no3-crater-lake-waters.htm 5. http://www.americaslibrary.gov/es/or/es_or_crater_1.html 6. http://www.summitpost.org/wizard-island-summit/157490 7. http://craterlaketrust.org/science-and-discovery/facts-and-figures 8. http://www.volcano.si.edu/world/volcano.cfm?vnum=1202-16-

Crater Lake and the melting glaciers

We’ve covered the interplay between melting glaciers and volcanic eruptions a couple times this month (see: http://tmblr.co/Zyv2Js1czF9-H). The presence of a thick ice cap can keep a lid on a volcano; increasing the pressure in the magma chamber so that its harder for gases to escape and increasing the pressure deep in the Earth so that less magma is generated in the first place.

Crater Lake has always struck me as an interesting possible example of this process. 7700 years ago, only a few thousand years after the end of the last glacial period, Mount Mazama, the formerly large volcano that sat on this site, tore itself to pieces in a huge volcanic eruption. That might have suggested a link between the end of the glaciers and the eruption, but it turns out that this eruption probably doesn't relate to the glaciers.

In fact, evidence from large volcanic arcs in Kamchatka and the Andes which had large ice caps during the last glacial cycle shows that there were large increases in volcanic activity around 10,000 years ago. Melting the glaciers was like popping the cork in a champagne bottle – the dissolved volcanic gases surged out as a series of eruptions.

Although the Mount Mazama eruption took place within a few thousand years of the melting of the glaciers, the Cascades don’t show the same pulse in volcanic activity. This could imply that the glaciers on the Cascades simply weren’t as big as the huge continental ice sheets.

The timing of Mazama's eruption and the end of the last ice age appears to be a concidence. Investigation of the rocks now exposed as layers in the caldera walls shows that the magma chamber developed over a period of several hundred thousand years. Different batches of magma arrived and built a large magma chamber; with the chemistry of erupted rocks changing each time a new batch arrived. That large magma chamber emptied suddenly 7700 years ago, opening a space in the ground that the peak collapsed into. That eruption formed the caldera that today is filled in by the clear, clean, crisp waters of Crater Lake.

-JBB

Image credit: Scott Smithson https://flic.kr/p/o3fFtc

Read more: http://bit.ly/1ztvqS2 http://on.doi.gov/1IqagKL

Phantom Ship Rock On foggy days or in low light conditions, this series of rocks that stick up out of Oregon’s Crater Lake give the appearance of being a wooden sailing ship, leading to its name. Crater lake sits in a Caldera at the center of Mount Mazama, formed 7000 years ago when the volcano underwent a huge eruption and the peak collapsed downward into the emptied magma chamber. Like all the other rocks you see, Phantom Ship Rock is made of igneous rocks; in this case, andesitic lavas. The lava in this structure is about 400,000 years old, predating the cataclysmic eruption by several hundred thousand years. Therefore, these rocks survived the giant eruption without being too heavily damaged, but they were exposed. The vertical “pipe” like pattern is a result of hydrothermal processes. During the volcano’s long lifetime, there have been many times when it wasn’t erupting, but when hot water was circulating through older volcanic rocks. Hot water flowing through these rocks led to the growth of new minerals, hardening them against erosion and creating the pattern that now plays tricks on our eyes. -JBB Image credit: Barb Mayer http://www.flickr.com/photos/11902536@N02/3939492962/ Science: http://pubs.usgs.gov/dds/dds-72/site/phant.htm http://www.learnnc.org/lp/multimedia/10570

Milky way over Crater Lake. While we have already covered the geology of this wonderful caldera in Oregon (see http://tinyurl.com/kxjthtq), we just had to share this photo of this place at night under the glow of the stars. Loz Image credit: Steve Ziegler