by Nick Parkins Friday, July 20, 2012
We live on a knife-edge, separated from an ocean of super-heated rock by a wafer-thin and perpetually rupturing crust, swinging our way through a cosmic minefield of lethal debris around a nuclear furnace prone to tantrums. For doomsayers, the end of the Mayan long-count calendar, set against such a backdrop, is a gift. Though Mayan culture never spoke of a cataclysm, Dec. 21, 2012 — the purported last day of a 5,125-year cycle in the Mesoamerican calendar — has been added to an endless list of days when the world has been predicted to end.
But what are our real chances of being wiped out by a cataclysmic event of the geologic sort — the kind that has happened in the past and will inevitably occur again someday? Let’s take a look at four of the most probable global catastrophes that could change life on Earth forever: asteroid impacts, super-eruptions, solar storms and earthquakes.
Atop the hit parade of life-ending risks are asteroids. In the past, asteroids have caused enormous damage and mass extinctions, such as the one that hit Mexico’s Yucatan Peninsula about 65 million years ago and finished off the dinosaurs. Detrital space junk continues to strike Earth all the time. Dust-, pea- and basketball-sized objects rain down daily. Car-sized objects veer into our atmosphere every few months. And abundant near-Earth objects (NEOs) the size of football stadiums float in orbits that overlap precariously with ours. The most recent large impactor was a 40-meter-wide rock that tore through the atmosphere over the Podkamennaya Tunguska River in Russia on June 30, 1908. The resulting air burst of 3 to 10 megatons laid waste to 80 million trees over 2,100 square kilometers of terrain and destroyed an area twice the size of Los Angeles (see story, p. 21).
Of greatest concern are the NEOs 1 kilometer wide and greater, including asteroids and comets, that have the potential to do the most damage. Data from NASA’s NEOWISE (NEO Wide-field Infrared Survey Explorer) spacecraft, which cataloged NEOs with diameters of at least 1 kilometer through early 2011, and from other sources are still being analyzed, but 910 such NEOs have been identified already. Scientists estimate that another 70 similar-sized NEOs are out there but haven’t been identified or tracked yet, says Donald Yeomans, manager of the Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory at Caltech. Scientists have also identified about 250 NEOs with at least a 2-kilometer diameter (closer to the probable threshold for globally catastrophic impacts), and scientists say there are probably another dozen yet to be identified. Once identified, the objects' speed, trajectory and threat can be tracked.
Threat level is categorized on the Torino scale, which characterizes the threat from large impactors over the next 100 years based on the likelihood of collision and the predicted level of impact. Two asteroids, 2007 VK184 and 2011 AG5, currently head NASA’s watch list, although both rate a lowly level 1 out of 10 in terms of their threat to Earth.
Level 10 events do happen. NEOs like the 10-kilometer-wide asteroid that struck the Yucatan tend to do so every 100 million years on average. The ensuing 100-million-megaton blast would cause fallout up to 4,000 kilometers away from the impact site and would flatten forests up to 1,800 kilometers away. Additionally, as was seen with the Chicxulub impact on the Yucatan, we could expect global wildfires. For months, day would turn to night as ash and debris clouded the atmosphere, causing permanent crop failures, plant death and cascading extinctions.
Objects 1 kilometer wide strike Earth a bit more often, roughly every 700,000 years. They strike with comparable force to the volcanic eruption at Indonesia’s Mount Tambora in 1815, the largest recorded in human history. An impact this size — potentially resulting from a large stony asteroid — in the mid-latitudes would cause major problems locally and globally. In addition to killing anything in its immediate vicinity, it would disrupt plant growth for months, causing some crop failures and other problems. Extinctions would be unlikely. And, Yeomans says, human casualties could be mitigated through evacuation planning and missions to deflect or disrupt the asteroid.
The threat posed from mid-sized objects larger than 100 meters has been reassessed in recent years. Astronomers now think there are about 20,500 such objects, about 45 percent fewer than originally thought, according to NASA. The majority of small or mid-sized objects remain unidentified, as NASA’s Spaceguard Survey has greater trouble identifying objects smaller than 100 meters wide, Yeomans says. “NEOs are often dark and relatively small, which makes them difficult to discover unless they make close-Earth approaches,” he says. But even with those, we have a bit of warning.
Most likely to strike Earth and cause damage in the short term are roughly 30-meter-wide objects similar to the Tunguska impactor simply because these are the most numerous, Yeomans says. If such an object were to hit land, it could cause local devastation but global devastation is not probable. Plus, the more likely scenario is that such objects would land in the ocean.
Ocean impacts are unlikely to produce devastating long-distance tsunamis, according to computational analyses by computer scientists Galen Gisler of the University of Oslo in Norway, and Robert Weaver and Michael Gittings of Los Alamos National Laboratory in New Mexico. Near-field effects may prove to be the greatest danger from mid-sized impactors — those equal to or less than 500 meters wide — in the ocean. Waves from an impact like this “could devastate shorelines within a hundred kilometers of the impact site,” the team wrote in a report presented at a conference on submarine mass movement and its consequences in Austin, Texas, in 2009. However, smaller impactors wouldn’t likely cause any damage.
No known NEOs currently pose a serious threat in the next 100 years, Yeomans says. Nonetheless, he says, we should prepare for the potential near-field consequences that would arise from unidentified small to mid-sized objects striking Earth. Of course, “the best defense remains to find threatening objects well in advance.” If we do that, and we find one that might eventually impact us, we’ll have years to prepare. Preparation might mean moving communities out of harm’s way, destroying the asteroid or employing techniques to slow or alter its trajectory so it misses Earth.
Summarizing a 2009 International Planetary Defense Conference in Granada, Spain, David Morrison, senior scientist at the NASA Astrobiology Institute in California, noted that several presentations had inflated the current risk of impact, with assessments that were based on faulty or misinterpreted data. “It is curious to see claims by policy analysts that the impact threat is increasing while the scientific community comes to the opposite conclusion,” Morrison noted in the summary for NASA. The Spaceguard Survey alone has eliminated at least 90 percent of the risk associated with impact by an unknown asteroid, he said.
Ever since the public became aware that a gigantic magma chamber, estimated at more than 10,000 cubic kilometers, underlies Yellowstone National Park in Wyoming, and that it has catastrophically erupted in the past, the doomsayers have been actively suggesting the volcano may be our undoing. Then, in November 2007, the doomsayers got a boost when scientists observed that the land in part of the park started inflating three times faster than ever before in recorded history. That uplift may have been caused by inflation in the magma chamber. Ever since, Yellowstone has taken its place in the collective consciousness as the scariest of the world’s known supervolcanoes.
Supervolcanoes are those capable of very large eruptions, producing 1,000 cubic kilometers or more of erupted material. “The largest Yellowstone eruption emitted 2,500 cubic kilometers of magma,” says Jake Lowenstern, of the U.S. Geological Survey in Menlo Park, Calif., and scientist-in-charge of the Yellowstone Volcano Observatory. Geologists have no idea how many such eruptions have occurred throughout geologic history as the geological record doesn’t provide enough solid evidence. Scientists do have a better record over the last 36 million years, though.
In a 2004 paper in the Bulletin of Volcanology, Ben G. Mason, then at the University of Cambridge in England, and colleagues stated that geologic evidence shows at least 42 super-eruptions with an explosivity magnitude of 8 or above have occurred over the last 36 million years, though there are likely more that have not been identified yet. A volcano is ranked based on the Volcanic Explosivity Index (VEI), a scale from 1 to 9. (For comparison, Mount Pinatubo’s 1991 eruption that caused a global cooling that year was a VEI 6.)
“Globally there has not been a super-eruption in 26,000 years,” Lowenstern says. The most recent one occurred on the North Island of New Zealand and the remaining caldera is now partially filled by Lake Taupo. As to our risk going forward, Mason and his colleagues found that based on their record of past eruptions, there is a 75 percent probability that a VEI 8 eruption will occur in the next 1 million years, with a 1 percent chance of one occurring in the next 460 to 7,200 years.
It is not clear whether Yellowstone is likely to erupt catastrophically again someday. The area remains seismically and volcanically active, with minor earthquakes occurring almost daily and strong steam explosions occurring every few years. Small-scale eruptions have occurred on dozens of occasions since the area’s last super-eruption 640,000 years ago, which blanketed much of the U.S. Midwest in ash.
Three large eruptions have occurred at Yellowstone, separated by relatively regular intervals of about 700,000 years. Simple math, some say, suggests Yellowstone is not blowing off steam. The largest eruption at Yellowstone was the Huckleberry Ridge eruption 2.1 million years ago; it released 2,500 cubic kilometers of volcanic debris and was 10,000 times larger than the 1980 Mount St. Helens eruption in Washington. (Recent research suggests this could have been two separate events, however.) Such an event would produce enough debris to bury an area the size of Texas 3.7 meters deep.
If Yellowstone were to produce another super-eruption, the consequences would be catastrophic. The most immediate threat to local communities are pyroclastic flows — super-heated avalanches of volcanic ash and debris that rapidly spill over the surrounding land. “They could potentially affect anyone living within 100 kilometers of Yellowstone,” Lowenstern says.
In cities like Cody, Wyo., that are downwind and close to the volcano, ash would also be a huge issue, starting to settle in just a few hours. “Heavy ashfall in the watersheds of major rivers like the Mississippi and Missouri would be carried downstream, ultimately affecting barge transportation and causing floods,” Lowenstern says. “It would interrupt agricultural production and could kill millions of livestock.” Modeling has shown that nationwide effects could include a light dusting of ash even in eastern U.S. cities, he adds. Even light ash can cause respiratory problems and can hinder power generation and water treatment.
A relatively small percentage of overall eruptive dust (fine ash) and aerosols could have significant impacts upon circulation in the atmosphere, affecting worldwide rainfall patterns and lowering temperatures by several degrees for a decade or more. This picture of potential climatic changes has been supported recently by calculations with a global circulation model by a group at the Max Planck Institute in Hamburg, Germany. Additionally, aerosol particles could catalyze ozone depletion, produce acid air pollution and potentially disrupt satellite transmissions, stated volcanologists Stephen Sparks of the University of Bristol and Stephen Self of Open University in the U.K., and colleagues in a 2005 report to the U.K. government’s Office of Science & Technology Natural Hazard Working Group.
Nevertheless, we would almost certainly have a good deal of warning before any such massive eruption, Lowenstern says. Instruments would record ground deformation, earthquake swarms, enhanced hydrothermal activity, enhanced degassing and other such precursors well before a super-eruption.
Yellowstone may be active, but that doesn’t mean it is likely to erupt any time soon. “Perhaps the abundant heat and gas discharge reflects its ability to calmly depressurize without building toward an eruption,” Lowenstern says. Other regions remain capable as well. “Taupo in New Zealand is one example, others are in South America, and we don’t know much about Toba in Indonesia,” he says. “Other volcanic regions may host large magma bodies that could serve as the source of future super-eruptions.”
In their report, Sparks, Self and colleagues estimated that the impact of a mid-sized super-eruption (such as one of these volcanoes) would be similar to a 1-kilometer-wide asteroid impact; it would likely cause local devastation but only minor global disruption. Nonetheless, we need to better understand the regional and global implications of large-magnitude explosive eruptions, with a focus on the effects of aerosol injections into the stratosphere using global climate models, the authors stated. Scientists should start, the team suggested, by inventorying potential supervolcanoes, which would provide a basis for identifying volcanic centers that should be studied more intensively.
Solar storms occur when the sun’s entangled magnetic field lines twist and snap, unleashing vast quantities of plasma and electromagnetic radiation. Space scientists are developing forecasts to predict upsurges in space weather up to one or two days in advance. Two major considerations distinguish solar storms from the events described above: First, unlike super-eruptions and giant impactors, solar storms are not going to cause physical devastation; instead, they could wreak havoc by disrupting or destroying communications systems, electrical grids and other infrastructure. Second, solar storms are perhaps the most likely hazard to cause problems on a global scale, largely because of their effects on society but also because they are fairly frequent.
The largest recorded solar storm, dubbed the Carrington Event, hit Earth in 1859, releasing energy from the sun equivalent to 10 billion atomic bombs. Though only a fraction of that energy hit Earth, geomagnetic activity triggered by the explosion electrified and incapacitated telegraph lines, which sparked fires and resulted in widespread communications disruption for months across North America and Europe.
In today’s highly connected and high-tech world, the results of such a storm could be severe. Satellites and other spacecraft would be bombarded by protons that produce glitches in astronomical data, affect operations of onboard electronic systems, and cause premature aging of computers, detectors and other spacecraft components. Such degradation to satellites would then affect everything that relies on satellite communications: GPS navigation; air traffic control and shipping systems; phones and computer networks; and all manner of financial and other systems, to name a few.
Arguably the biggest threat is to power grids, according to John Kappenman of Metatech Corporation, a California-based company that studies the effects of electromagnetic disturbances, especially on communications systems. Metatech recently assessed the risks facing the U.S. and North America from solar storms. Nationwide blackouts and lengthy restoration times are a distinct possibility, the company found. “Many of the things that we have done to increase operational efficiency and haul power long distances have inadvertently and unknowingly escalated the risks from geomagnetic storms,” said Kappenman at a 2008 National Academy of Sciences workshop on severe space weather events.
Power grids are susceptible to geomagnetically induced currents (GICs) that can trip breakers, overload circuits, and saturate and fry transformers. Repair could easily take a year or more, Kappenman said at the workshop. Interdependent infrastructure like water treatment and distribution systems would suffer as well. Once the power goes out, perishable foods and medications would spoil, heating and air conditioning systems would fail, sewage disposal would halt, and transportation and fuel supplies would be affected. Even smaller storms can cause problems, such as the Halloween storms of October and November 2003, which caused power outages, impacted communications systems and forced planes to be rerouted.
Currently, the U.S. is not equipped to weather an event like the Carrington storm, Kappenman noted. Were one to hit tomorrow, according to Kappenman, the aftermath could last several years and cost trillions of dollars. The U.S. has ways to mitigate such damage, though, including simple and cost-effective measures like installing neutral ground resistors that would decrease grid GIC levels by 60 to 70 percent.
“Many experts believe Carrington is around a 1-in-100 year event, and that other severe events have occurred such as in 1921 when the telephone exchange burned down in Karlstad, Sweden,” says Mike Hapgood, head of the space environment group at the Rutherford Appleton Laboratory in Didcot, U.K. Hapgood suggests that we should prepare for a much larger storm, the kind likely to hit once every thousand years. In a recent comment in Nature, Hapgood proposed ways to prepare, such as by digitizing old space weather data, placing a greater emphasis on statistical studies and developing models that could help operators of at-risk systems such as airlines and power grids to make informed decisions.
Arguably the most likely life-altering hazard we face is a major earthquake; earthquakes occur with regularity all over the world. On average, 17 magnitude-7.0 or larger quakes occur each year, with at least one quake registering magnitude-8.0 or greater. Even magnitude-5.0 and 6.0 earthquakes can cause major damage, depending on where they hit; roughly 1,300 magnitude-5.0 to 5.9 quakes occur around the world each year. Quakes can devastate a city or even a region or country, as we’ve seen in places such as Haiti with the magnitude-7.0 quake in January 2010 and Japan with the magnitude-9.0 quake that struck in March 2011. But even the largest quake in the world would not cause global damage.
For large cities on big fault lines, research and preparation are paramount. Unlike large volcanic eruptions, earthquakes typically occur with little warning, and the resulting seismic waves travel at speeds of 3 kilometers per second, nearly 10 times the speed of sound in air.
That means, for example, that a major rupture on the southern San Andreas Fault far south of Los Angeles would strike the city without advance warning — a scary proposition for Southern Californians who live along one of the world’s longest, most active fault lines. “The question is not if but when Southern California experiences a major earthquake — one so damaging it will permanently change lives and livelihoods in the region,” wrote Suzanne Perry, staff scientist of the Science Application for Risk Reduction project at USGS in Pasadena, Calif., and colleagues in a 2008 USGS circular report titled “The ShakeOut Earthquake Scenario — A Story That Southern Californians Are Writing.”
The last major rupture on the southern San Andreas Fault, dated about 1690, is believed to have occurred on 150 kilometers of fault between Coachella and Wrightwood. The ShakeOut Scenario considered what would happen if a hypothetical magnitude-7.8 quake occurred along that stretch of the fault, starting at Bombay Beach on the Salton Sea, the section of the fault with the greatest risk of rupture over the next 30 years. A quake of this size could affect an entire region at once, Perry says, unlike the magnitude-6.7 Northridge quake in 1994 that disrupted some neighborhoods but left others nearby unharmed.
According to the scenario, a rupture at Bombay Beach would shoot northwest up the Coachella Valley, instantly striking at regional transportation routes like Interstate 10, communication lines and pipelines that cross this area. State highways that have been seismically retrofitted (at a cost of $6 billion) may survive, but damage to local roads, bridges and overpasses could take weeks to months to fix.
Buildings that have been built strictly to code may stay upright, but the thousands that aren’t built to code or haven’t been retrofitted yet would likely crumple throughout many towns, including Los Angeles and San Bernardino. Electrical power disruption could cause chaos, and could topple water treatment and sewage systems and communications networks. But “the biggest long-term problem is extended disruption to the water conveyance system,” Perry says.
“In communities with proactive disaster planning, rebuilding can begin without delay,” Perry says. But even some well-prepared communities, such as Christchurch, New Zealand, which has been hit by several large quakes and thousands of aftershocks over the last two years, would struggle with a quake that size — especially with ongoing aftershocks.
Resilient societies would bounce back quickly and recover within a few years, while those that are less resilient would take longer, and some may never fully recover. “In 2010, the magnitude-7.0 Haiti earthquake caused enormous, long-lasting devastation, while the [magnitude-] 8.8 Chile quake, which released nearly 1,000 times more energy, saw relatively modest levels of destruction,” Perry says. Chile was better prepared to start with, and “Chilean society is more resilient to disasters.”
Adequate investment, planning and preparation can identify necessary and realistic precautions that individuals, schools and businesses can take, alongside actions by organizations, communities and governments — that’s a large part of the goal of the ShakeOut drills. Fortunately, in many cases, scientists know where earthquakes are most likely to strike and therefore which communities should prepare for such events, Perry says. Of course, preparation has costs and officials have to work with cost-benefit analyses; it’s not always practical to retrofit entire communities.
Most world-changing events that punctuate the vast prehistory of our planet are lent exaggerated immediacy by prophets of doom. Scientists who study such events concede that these hazards can change lives when they occur. However, the highly infrequent nature and scale of total threat posed make preparation for all potential hazards an unrealistic, impractical and impossible venture. It is fortunate that truly global catastrophic events are rare.
That said, realistic fears surrounding local and regional threats posed by small to mid-sized asteroids and volcanic eruptions, and larger earthquakes and solar flares, can often be addressed, and in some instances, dismissed with sustained research. The Spaceguard Survey and the ShakeOut drills have shown that we may profit from scientific advancements through enhanced understanding and sense of well-being, as much as through preparation and the prevention of human or material loss.
Perhaps, if the December 21, 2012, infers a passing, it is not of a world but an age, as the time comes when we understand our home as not something to fear, but rather to appreciate and respect.
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