Rapid Earth Changes in Historic Times
What happened to the Sahara desert? What’s going on in Java, man? Geologists are surprised sometimes by recent major changes.
Science Daily asks an intriguing question about something most people probably don’t know: “6,000 years ago the Sahara Desert was tropical, so what happened?”
As little as 6,000 years ago, the vast Sahara Desert was covered in grassland that received plenty of rainfall, but shifts in the world’s weather patterns abruptly transformed the vegetated region into some of the driest land on Earth.
For scientists trained to think in millions of years, that’s a huge change in the ‘geological blink of an eye,’ as they are wont to say. Scientists from Yale and from Texas A&M think it’s due to changes in prevailing winds that affected rainfall, but why so permanent? This is climate change you can’t blame on fossil fuels. “We know that 6,000 years ago, what is now the Sahara Desert was a rainy place,” says Robert Korty from Texas A&M.
Science Magazine discusses one Fidel Costa—not Castro—who reads crystals. He is studying a volcanic eruption that occurred 4,000 years ago in Indonesia. Costa tries to read clues from crystals as small as lentils about why the Gede volcano erupted so quickly, to figure out when it might erupt again.
Already, the few researchers adept at using the technique have found that magma can tear through the crust at searing velocities, and that volcanoes can gurgle to life in a geologic instant. Instead of taking centuries or millennia, these processes can unfold in a matter of decades or years, sometimes even months, says Kari Cooper, a volcano geochemist at the University of California, Davis.
How quickly can things change underground to affect the surface? In just months or days, magma lurking in chambers can “mobilize rapidly,” the teams reported in the article say. Just because scientists can’t detect magma chambers easily doesn’t mean volcanoes like Mt. Hood don’t endanger nearby population centers. Within a century or less, magma from long-dormant volcanoes can start moving. In fact, “vats of liquid magma may only exist immediately prior to an eruption.”
They have found that slugs of magma can rise 10 kilometers in roughly 10 minutes. “It’s like a freight train,” she says.
The new “mush model” represents a change in thinking less than a decade old. It “suggests that magma may liquefy and erupt even more quickly than many researchers thought.” Reporter Julia Rosen quotes scientists calling the new model a “game changer” and a “surprise” that indicates to laypeople that even the experts can undergo rapid changes in thinking.
See also Calvin Miller’s paper in PNAS, “Eruptible Magma,” about geophysicists’ frustration trying to locate magma chambers under volcanoes. There are “Key questions to be addressed if we are to understand magma systems and the eruptions that they produce,” he says. Some geologists are suspecting that “durations within the eruptibility window are interpreted to be short to extremely short” on the range of one to 10,000 years.
So when volcanologists find anomalies, we begin to understand that maybe there’s a lot they don’t understand. For instance, a press release from Washington University in St. Louis wonders “What’s up with Madagascar?” Specifically, “Why are there volcanoes on an island that isn’t near any tectonic boundaries?” That’s a clue of an impending eruption in a dormant paradigm. The article speaks of millions of years, but how certain can anyone be with this kind of talk?
Madagascar, the big island off the east coast of Africa with the lemurs and baobabs, is thought to be sitting in the middle of an old tectonic plate, and so, by the rules of plate tectonics, should be tectonically quiet: few earthquakes and no volcanoes.
But it’s not. The island has been away from tectonic action for the past 80 million years, said Martin Pratt, research scientist in earth and planetary sciences at Washington University in St. Louis, yet it experiences about 500 earthquakes per year.
The island also has volcanoes that have been active within the recent geologic past. “Having active volcanoes in Madagascar is like having erupting volcanoes in St. Louis,” said Michael Wysession, professor of earth and planetary sciences. “You have to ask yourself, ‘What are they doing there?’”
The hero of the story is quick on his storytelling: “150 million years ago,” blah blah blah, then “90 million years ago,” stuff happened. An invisible slab fell off the mantle. He’s got it all figured out – till the next paradigm shift.
Update 12/07/16: Greenland lost up to 90% of its vast ice fields several times for extended periods, according to an article on Live Science. Although the article mentions millions of years, it also speaks of “massive and rapid ice loss.” Once again, this kind of change was unexpected; “its surface ice was more variable than once thought.” The article does not mention warm periods from history in the time of the Vikings, who lived and farmed along Greenland’s coast. Long before the Industrial Revolution, these times of “green land” could not have been due to anthropogenic global warming.
For more on Greenland’s ice sheet dynamics, see Phys.org, Science Daily, and another Science Daily piece. Two papers in Nature go into detail: #1 about extended ice-free periods in the Pleistocene, and #2 about “rapid and global changes” in the Greenland ice sheet.
And Greenland is not alone. Another research summary in Nature says “As Earth emerged from the last ice age more than 10,000 years ago, West Antarctica … warmed two to three times faster than the rest of the planet.” See also Science Daily‘s report, “Information theory offers new way to read ice cores.” Readers may not be aware that ice core data is “packed with noise and error, making the climate story hard to read.”
Update 12/16/16: The BBC News makes an astonishing claim about one of the driest places on earth: Chile’s Atacama Desert. It once had lakes and wetlands. Was that millions of years ago? No; just thousands. In fact, “the region may have been habitable for early settlers.” Live Science says there is new archaeological evidence for settlements there that no one had bothered to look for before. There are also fossils of marine life deep in the sediments. See photos on Phys.org of how the desert looks today. It gets 15mm of precipitation per year now; some parts get none.
You can measure crystals in the lab today, and hike around Madagascar in the present. That doesn’t give you a crystal ball into mythical worlds in deep time. There’s something really significant about that phrase, “than many researchers previously thought.” Remember, what they previously thought was gospel truth, taught in the textbooks. So when is the next “whoops” moment?