Sunday, August 26, 2007

Mega Events in Geological History

A "black mat" of algal growth in Arizona marks a line of extinction at 12,900 years ago; Clovis points and mammoth skeletons were found at the line but not above it.
Credit: Allen West, UCSB via the National Science Foundation

NOVA has a program titled Mystery of the Megaflood.
"About 15,000 years ago, in the waning millennia of the Ice Age, a vast lake known as Glacial Lake Missoula suddenly burst through the ice dam that plugged it at one end. In the space of just 48 hours, geologists believe, the collapse sent 500 cubic miles of water cascading across the Pacific Northwest, creating overnight such unusual landscapes as the scablands of eastern Washington."
Lake Agassiz was an immense lake, bigger than all of the present-day Great Lakes combined, theorized to be in the center of North America at the end of the last ice age. In another mega-event, perhaps 7,500 to 8,500 years ago:
Much of the final drainage of Lake Agassiz may have occurred in a very short time — perhaps as little as one year — and may have been responsible for the "8.2 kyr event", a cooling episode of Earth's climate, visible in ice cores and other climate records.
That is, the huge flow of fresh water into the North Atlantic may have shut off the Atlantic circulation, causing a significant change in weather over much of Europe and other parts of the globe.

Scientists are discovering or suggesting the existence of more and more ancient mega-events. Something, perhaps a comet caused fires that raged over much of the North American continent some 13,000 years ago, apparently causing the extinction of many species.

In 1998, William Ryan and Walter Pitman, geologists from Columbia University, suggested that about 5600 BC, as sea levels rose, the rising Mediterranean spilled over a rocky sill at the Bosporus. The event flooded 60,000 mile² (155,000 km²) of land and significantly expanded the Black Sea shoreline to the north and west. Ryan and Pitman wrote:
"Ten cubic miles [42 km³] of water poured through each day, two hundred times what flows over Niagara Falls. …The Bosporus flume roared and surged at full spate for at least three hundred days."
We don't often think of the Columbian Exchange in these terms, but after Columbus established sea connection between the old and new worlds there was a mega-environmental event. There was a human population crash in the Americas, and invasive species (including man and domesticated species) competed with indigenous species and radically changed the landscapes worldwide.

The Yellowstone volcano had a major eruption approximately 650,000 years ago:
The caldera that it left is 53 miles long and 28 miles wide. In the area surrounding Yellowstone, 3000 square miles were subjected to a flow of pyroclastic material composed of 240 cubic miles of hot ash and pumice. Ash was also thrown into the atmosphere and blanketed much of North America. It can still be identified in core samples from as far away as the Gulf of Mexico.

Since this occurred more than a half million years ago this is all ancient history, right? Not quite. Yellowstone continues to be geologically active even today. Smaller explosions caused by hydrothermal activity (water or steam heated in an underground chamber until the top blows off) have been much more common and recent in Yellowstone's history than the massive caldera-forming eruptions. One of these happened as recently as 13,000 years ago, creating a three-mile wide crater that is now a portion of Yellowstone Lake called Mary Bay. Also, smaller volcanic eruptions with flows of lava, ash and pumice have occurred. Flows like these have filled in much of the old caldera since its creation.

Another catastrophic eruption is also possible. The effects of such a disaster are hard to even comprehend. Bill McGuire, professor of geohazards at the Benfield Greig Hazard Research Centre at the University College of London told the UK Daily Express, "Magma would be flung 50 kilometers into the atmosphere. Within a thousand kilometers virtually all life would be killed by falling ash, lava flows and the sheer explosive force of the eruption. One thousand cubic kilometers of lava would pour out of the volcano, enough to coat the whole USA with a layer 5 inches thick." He adds that it would once again bring "the bitter cold of Volcanic Winter to Planet Earth. Mankind may become extinct."
According to Wikipedia:
The Little Ice Age brought bitterly cold winters to many parts of the world, but is most thoroughly documented in Europe and North America. In the mid-17th century, glaciers in the Swiss Alps advanced, gradually engulfing farms and crushing entire villages. The River Thames and the canals and rivers of the Netherlands often froze over during the winter, and people skated and even held frost fairs on the ice. The first Thames frost fair was in 1607; the last in 1814, although changes to the bridges and the addition of an embankment affected the river flow and depth, hence the possibility of freezes. The freeze of the Golden Horn and the southern section of the Bosphorus took place in 1622. The winter of 1794/95 was particularly harsh when the French invasion army under Pichegru could march on the frozen rivers of the Netherlands, whilst the Dutch fleet was fixed in the ice in Den Helder harbour. In the winter of 1780, New York Harbor froze, allowing people to walk from Manhattan to Staten Island. Sea ice surrounding Iceland extended for miles in every direction, closing that island's harbors to shipping.
Krakatau erupted in 1883, in one of the largest eruptions in recent time. The 1883 eruption ejected more than 25 cubic kilometres of rock, ash, and pumice [1], and generated the loudest sound historically heard thousands of miles away.
Ash fell on Singapore 840 km to the N, Cocos (Keeling) Island 1155 km to the SW, and ships as far as 6076 km WNW. Darkness covered the Sunda Straits from 11 a.m. onthe 27th until dawn the next day.

Giant waves reached heights of 40 m above sea level, devastating everything in their path and hurling ashore coral blocks weighing as much as 600 tons....

Fine ash and aerosol, erupted perhaps 50 km into the stratosphere, circled the equator in 13 days. Three months after the eruption these products had spread to higher latitudes causing such vivid red sunset afterglows that fire engines were called out in New York, Poughkeepsie, and New Haven to quench the apparent conflagration. Unusual sunsets continued for 3 years.....

The volcanic dust veil that created such spectacular atmospheric effects also acted as a solar radiation filter, lowering global temperatures as much as 1.2 degree C in the year after the eruption. Temperatures did not return to normal until 1888.
People do not often think in terms of 100 years, much less in terms of 1000 years, and so we tend not to recognize that mega-events are really possibilities rather than the stuff of scary movies -- no more real than vampires, or werewolves, Freddy Krueger or Jason of Friday the 13th. The records indicate however that they are real and do occur with distressing frequency. Social planning should take them into account, if not your individual planning of that of the nuclear family.

I suspect that we are facing anthropogenic environmental catastrophes of this magnitude by the end of the 21st century, and that we must begin to act now and act with continuing responsibility to ameliorate the damage and the consequences. If we fail to recognize that catastrophic events are not uncommon on such time scales, it is hard to mobilize the will to act.

There are people who do not believe the scientific record, preferring to believe the interpretation of the bible that says the earth was created as it now exists several thousand years ago. They will have great difficulty believing that we face a catastrophe of our own making. Fortunately, there are not only secularists but other evangelical co-religionists willing to take on these true believers and argue them into a stewardship of the earth.

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