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Thor's Well, OR -

This phenomenon, causing a gaping, seemingly bottomless sinkhole, is caused by a hole in the rock that sucks in the water around it.

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Thor's Well, OR -

It works kind of like a black hole. Located just off the coast of Cape Perpetua, Thor’s Well is more impressive at high tide or during storms. But beware—this spectacular sight can also be deadly.

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Nacreous Clouds, AK -

Also known as polar stratospheric clouds or mother of pearl, these clouds occur during winter at altitudes of 49,000 - 82,000 ft.

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Nacreous Clouds, AK -

These ethereal-looking clouds need a low temperature to exist, at least -108°F, which means that the only place to spot them in America is Alaska.

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Ice caves, Mendenhall Glacier, AK -

To access the 12-mile-long glacier in the Mendenhall Valley, visitors have to first kayak there and then climb over ice.

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Ice caves, Mendenhall Glacier, AK -

This impressive sight is unfortunately receding thanks to rising temperatures. The Mendenhall Glacier has receded almost two mi since 1958, which is a big increase from the 0.5 mi it receded between 1500 and the 1950s.

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Eternal Flame Falls, NY -

A small waterfall in upstate New York hides a big surprise. Hidden behind a water stream in a cave, an eight-inch-tall flame burns all year long.

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Eternal Flame Falls, NY -

A natural gas leak feeds the flame, which does eventually blow out. Hikers in the area take on the responsibility of re-lighting it when needed.

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Fly Geyser, NV -

This geyser’s geological formation and naturally occurring steam give it a distinct whimsical look.

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Fly Geyser, NV -

The property on which the geyser is located was purchased in 2016 by the non-profit Burning Man Project for $6.5 million. This means that the attendees of the Burning Man festival in the Black Rock Desert will likely be able to visit this geothermal geyser in the near future.

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Fireflies, TN -

For two weeks in the late spring, the state’s Great Smoky Mountains serve as the stage for an incredible spectacle. During this period, one species of firefly glows continuously.

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Fireflies, TN -

Scientists are unsure of the reason behind the insects choice to flash synchronously. One of the leading theories suggests that the behavior is related to competition between males to be the first to flash or produce the brightest bioluminescence.

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Psychedelic Swamp, FL -

The technicolor effect in this swamp isn’t thanks to Photoshop or filters, but due to the release of tannic acids from decomposing plants in the water.

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Psychedelic Swamp, FL -

Cypress leaves release natural oils into the water, which produce a type of “oil slick” effect. This causes the sunlight to produce a psychedelic rainbow on the swamp’s surface.

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Fire rainbows, ID -

Despite its name, this phenomenon has nothing to do with fire. Officially known in weather-savvy circles as a circumhorizontal arc, this rare sight isn’t produced by the same process as rainbows.

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Fire rainbows, ID -

They are the product of light passing through wispy, high-altitude cirrus clouds.

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Devil's Kettle, MN -

Where does the water go? Does it just vanish? This phenomenon has puzzled, and continues to puzzle, scientists for a long time. The Brule River splits at the Devil’s Kettle waterfall, with half of it continuing on its merry way while the other half seemingly just pours into a hole.

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Devil's Kettle, MN -

However, a researcher from the Minnesota Department of Natural Resources claimed in 2017 that he believes this to be an optical illusion, and that half the river isn’t dribbling into the center of the earth after all.

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Rain bombs, AZ -

These wet microbursts can produce winds of more than 150 mph.

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Rain bombs, AZ -

These sights occur during thunderstorms when rain clouds full of water droplets or hail mix with patches of dry air.

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Yellowstone’s rainbow hot springs -

The largest of these springs is called, for obvious reasons, the Grand Prismatic Spring. This is due to the high temperature of the water released, which hosts a series of colorful bacteria that get their colors from different photosynthetic processes.

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Yellowstone’s rainbow hot springs -

The spring was officially discovered by the Hayden Expedition in 1871 during the first federally-funded Yellowstone expedition.

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Pando tree, UT -

Also known as the Trembling Giant, what appears to be an assortment of trees actually happens to be one tree, and is believed to be among the oldest known living organisms.

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Pando tree, UT -

This single male quaking aspen has one massive underground root system, making it seem like it’s separate individual trees. Occupying 106 acres, Pando is located southwest of Fish Lake on Utah State Route 25.

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Fire devils, VA -

Also known as fire whirls or fire tornadoes, these rare occurrences are also very dangerous due to their erratic nature. For these to form, the conditions have to be ideal: extremely hot and windy. These conditions allow the atmosphere to work in a similar way to a toilet flushing.

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Gravity Hill, PA -

Also known as a magnetic hill, mystery hill, mystery spot or gravity road, these places produce an optical illusion in which slight downhills appear to go uphill.

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Gravity Hill, PA -

Because of this effect, objects appear to roll uphill when they’re actually going downhill. Gravity Hill attracts a number of curious folks.

See also: The world's strangest natural wonders

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