7Uturuncu
Photo credit: Rojk/Wikimedia
Uturuncu, a 6,000-meter (20,000 ft) volcano in southwest Bolivia, last erupted 300,000 years ago. Satellite observations from the last 20 years have found the volcano’s underground chamber filling up 10 times faster than similar volcanic systems. It’s growing by a cubic meter (35 cubic feet) of magma per second. The result is that the land around the volcano in an area 70 kilometers (43 miles) across is ballooning upward by a couple of centimeters every year.
The first unanswered question is how long the inflation has been going on. Geomorphologists have studied nearby terrain and it looks to be a relatively recent phenomenon, but there’s a lot of detective work left.
The other mystery is what Uturuncu will do in the future. Oregon State University’s Shan de Silva, who’s been studying the volcano since 2006, thinks it could be a potential supervolcano. Other geologists see no evidence for that claim. Either way, 300,000 years is about the average wait between eruptions in southwest Bolivia, and Uturuncu looks like it’s getting ready to do something.
6The Permian Extinction
Photo credit: Vassil/Wikimedia
The most intense extinction in Earth’s history was the End-Permian mass extinction. An estimated 93–97 percent of species on the planet were wiped out. The cause of the extinction is one of the biggest debates in paleontology.
Meteorites are an obvious suspect. A possible impact crater in Antarctica has been suggested, but in general, the evidence for a collision is weak.
Volcanoes are a popular suggestion, the most likely candidates being the Siberian Traps which formed around that time. Scientists studying the extinction boundary in Canada found a layer of coal ash. They suggest volcanism set alight vast swathes of coal, causing a runaway greenhouse effect. Even without the coal fire, the volcanoes could have spewed sulfate into the air to block out the sun and create torrents of acid rain.
Volcanism could have played a more subtle role. A team of MIT researchers have pointed the blame at a microbe named Methanosarcina. These single-celled archaea produce methane and thrive on nickel and carbon dioxide—both of which were abundant due to volcanoes. Methane is 30 times more potent than carbon dioxide as a greenhouse gas and could have caused devastating warming of the planet.
5Lake Hillier
Lake Hillier is not the only pink lake in the world, but it’s definitely the least understood. It was discovered in 1802 in a pristine area of Australia’s wilderness. To protect wildlife that live around the lake, it’s currently only possible to view it from the air. This isolation has left it unstudied.
The “bubblegum pink” lake is safe to swim in, though it’s extremely salty. There are three likely causes for the color, based on what we know of other pink lakes around the world.
Pink Lake in Western Australia is actually less pink (and in hillier terrain) than Lake Hillier. Pink Lake’s color is caused by a combination of shrimp and microorganisms known as halobacteria (which aren’t really a type of bacteria). There may be actual bacteria, or Achaea such as the misnamed halobacteria, living in Hillier’s salt crusts.
Lake Retba in Senegal is a similar color and shares a high salt content, but its pinkness is caused by algae.
Finally, Hillier’s color may not require life at all but could be due to chemical reactions. The salt in the lake could react with dissolved baking soda, or there could be some other unique composition of rock surrounding the lake.
One option that’s definitely ruled out is an optical illusion, as the water stays pink even when placed in a bottle.
4How Hawaii Formed
The Hawaiian Island chain is one of many believed to have been formed by a “hot spot.” These are regions where magma rises to the surface and stays in place for tens of millions of years as continental plates drift over them. In doing so, they produce rows of volcanic islands, with an active volcano located on the youngest of them. These make up the 5 percent of volcanoes located far from plate boundaries.
The cause of these hot spots is one of geology’s biggest mysteries. The leading theory is a plume of hot magma rising from as far down as the border between the Earth’s mantle and inner core, 3,000 kilometers (1,800 mi) deep. These are known as mantle plumes, but there’s no consensus as to whether they actually exist. Lab experiments and theoretical models suggest they are at least possible
In 2011, an MIT team published a study suggesting a thermal anomaly 725 kilometers (450 mi) west of Hawaii was a more likely candidate and may have been only 800 kilometers (500 mi) below the surface. This trapped pool of molten materials then traveled across the top of the mantle before rising through the crust.
3The Grand Canyon’s Age
The Grand Canyon is one of the most famous geological formations on Earth. It’s also one of the most studied. Despite that, there is no consensus on how old the canyon is, and the quibble’s not over just a few years. Scientists on one side are pushing an age of around six million years. On the other side, they’re saying 70 million.
The two camps disagree about whether the canyon was carved by the Colorado River or whether it was already there and the Colorado simply routed its way through. Authors continue to publish papers supporting each hypothesis without making much progress.
2Low-Angled Normal Faults
Photo via R.W. Allmendinger/Cornell University
A fault is a crack in the Earth’s surface, and the sides of the fault can move against each other in any direction. They’re rarely vertical, and the side that rests on top is called a hanging wall. The lower half is the footwell. A slip-dip fault is one where the hanging wall slides up or down the footwell, and these faults are normally very steep.
Slip-dip faults whose hanging wall slides downward are known as normal faults. Normal faults that have a shallow slope less than 30 degrees from the horizontal are low-angle normal faults, or LANFs. And LANFs are a problem because they shouldn’t exist. Our models say that if they form they should seize up and turn into steeper faults. They’ve been called “the greatest paradox of tectonics.”
LANFs should lock because the friction between the two sides should stop them moving. Normally, when a fault locks, it strains until it violently overcomes the friction in an earthquake. Yet LANFs have never been confirmed to cause earthquakes, and it looks likely they might not do so. That makes them the only known class of faults to move solely by gradual creep.
This all means there are significant holes in some importantly geological models. Alternatively, our lab measurements of fracture and friction simplydon’t translate to the real world the way we think they do.
1Messinian Salinity Crisis
Around six million years ago, the Mediterranean Sea turned into a desert. It stayed that way for around 630,000 years, an era now known as the Messinian Salinity Crisis. Scientists agree that it was almost certainly because the sea became blocked from the Atlantic. The mystery is why, and there’s no shortage of theories.
One idea is that an expansion of the polar ice caps lowered sea levels and created a shallow piece of land to block the ocean’s access. Alternatively, tectonic collisions may have raised the seabed near Gibraltar, the way they raised the nearby Alps. These movements could have instead squeezed together Spain and Morocco to close the strait.
A more unusual theory put forward by geologists at Royal Holloway University of London is that the floor of the Atlantic ocean peeled up. The resulting flap, still attached to the ocean floor at its western end, let out lighter rocks from underneath. These floated into place to create a giant natural dam across the Gibraltar strait, until the sea flooded again suddenly half a million years later.
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