Supervolcano caused global cooling

The supervolcano which erupted 74,000 years ago at Toba in northern Sumatra was the most devastating natural event ever witnessed by humans. Now new evidence has emerged that the blast had long term implications for global ecosystems as it led to many years of drought, caused by a dramatic and prolonged drop in global temperatures.

Beautiful but deadly, and nowhere near the size of the Toba eruption, 74,000 years ago. Image Credit: Flickr/Roberto Zingales

An international team of researchers have shown that the forests which covered India before the volcanic eruption were replaced by open scrubland, and moisture-loving plants like ferns disappeared. The results suggest the global climate became much colder and, consequently much drier, which destroyed forests that depended on warm moist conditions.

To make their discovery, the researchers analysed long vertical sections of soil and marine sediment, called cores. The Toba eruption blew so much ash and rock into the atmosphere that it forms an easily-distinguished layer in soil and sediment cores from much of southern Asia. This meant the researchers could easily identify pre- and post-eruption deposits of soil and sediment and analyse their composition.

The researchers used the ratio of different carbon isotopes found in soil layers deposited before and after the eruption to examine the effect it had on vegetation that grew in India. Different types of vegetation leave different signature ratios of carbon isotopes in the soil because they use different chemical pathways to produce food through photosynthesis. The change in carbon isotope ratio showed that the vegetation changed from lush tropical forest to open scrubland just after the eruption occurred.

They also found much less pollen from ferns, which prefer warm, wet conditions, in marine sediment from after the eruption, suggesting there were far fewer of these plants alive at the time.

The Toba eruption was the most powerful volcanic eruption on Earth in the past two million years, causing temperatures to fall and resulting in massive droughts, which lasted for almost two thousand years!  It’s easy to why scientists have suggested deliberately pumping tonnes of sulphate particles, just like those produced by volcanic eruptions such as Toba, into the upper atmosphere to reduce global temperatures in the face of anthropogenic climate change.

Paper Reference: Williams, M., et al (2009) ‘Environmental impact of the 73 ka Toba super-eruption in South Asia’. Palaeogeography, Palaeoclimatology, Palaeoecology. doi:10.1016/j.palaeo.2009.10.009

Geology aids quest for ancient Egyptian tombs

Lara Croft should take a geologist along with her next time she goes in search of lost Egyptian tombs, according to research findings presented to a meeting of the Geological Society of America this week.

A water-damaged ceiling means this tomb's occupant is not going to be happy! Image: Katarin Parizek, Penn State

Understanding the geology of the Valley of the Kings in Luxor, Egypt, led to the discovery of a new tomb and is helping archaeologists protect known and unknown tomb sites from potentially-devastating water damage.

The researchers found that 30 of the 63 known tombs in the Valley of the Kings were built below ‘fracture traces’. Fracture traces are found above areas of broken, fractured rock, which is much easier to excavate than solid rock. As a result, ancient tomb-builders in the Valley of the Kings tended to favour these areas as tomb sites.

By searching specifically around known fracture traces, a new tomb was uncovered by archaeologists in February 2006 lying next to a fracture trace that had earlier been mapped. Egyptian archaeologists are now using geological data, combined with traditional archaeological clues, to hunt for even more undiscovered tombs and their archaeological treasure.

Fracture traces may be helping to find new tombs, but they could also be putting many tombs at risk of water damage. It may be easier to dig through, but when it rains water can seep through the broken rock and into the tombs, destroying priceless painted walls and ceilings.

Archaeologists can try to redirect flood water away from vulnerable tombs, and understanding the geology of the Valley will allow them to avoid inadvertently redirecting water into any as-yet-undiscovered tombs beneath other fracture traces. The researchers who reported the findings are working to map and photograph the tombs in the Valley of the Kings in an attempt to preserve a record of this famous historical site.

‘Fossilised’ supervolcano reveals hidden secrets

Scientists from the USA and Italy have found the fossilised form of a long-buried supervolcano preserved in rocks in the Sesia valley, Italy. An unusual contortion of the Earth’s crust exposed the fossil supervolcano, allowing scientists to see for the first time the hidden plumbing that feeds volcanic eruptions.

Inside the caldera at Lake Toba, Indonesia. It looks peaceful from here, but what's happening deep below? Image: Wikimedia/Tbachner

The supervolcano in Sesia valley was revealed by the movement of the Earth’s tectonic plates, which make up the crust of our planet. As the African plate drifted northwards towards Europe, a piece of crust in modern-day Italy was pushed upwards, bringing the fossilised volcano to the surface. It exposed not only the 13-kilometre-wide crater, or caldera, of the volcano, but the 25-kilometre-deep plumbing system beneath it. The tracks left by magma forcing its way to the surface are clearly visible in the rocks, and gave the scientists a unique opportunity to see “inside” one of nature’s most powerful forces.

Supervolcanos, such as the one buried beneath Yellowstone National Park in the USA, have the potential to cause global catastrophe. Supervolcanic eruptions are caused by the explosive eruption of gas from molten rock oozing towards the surface, which throws thousands of cubic metres of rock and ash into the air. Our ancestors witnessed one such event 74,000 years ago when a supervolcano erupted under Lake Toba, in Indonesia. The ash and sulphur dioxide it released caused the global temperatures to drop by 3 – 5^oC, wiping out plants and the animals that depended on them. Research suggests 60% of the people alive at the time were killed.

The new discovery in Sesia valley will help scientists to understand what drives the devastating eruption of a supervolcano, and perhaps develop ways to predict when we may next see such an eruption occur.

Paper reference: doi: 10.1130/G30003A.1

How to hide from an earthquake

Earthquakes are one of the most destructive forces known to man. When one strikes, it twists the very ground we walk on, sending great rippling shockwaves across a massive area. It is these waves that cause the most damage, literally shaking buildings apart.

Yet scientists now believe it is possible to protect our most important buildings, such as hospitals, from the devastating shockwaves caused by earthquakes. By using metamaterials – materials made from many different substances layered together – the waves can be redirected around the protected structure, keeping it safe from harm.

The proposed earthquake defence works in exactly the same as an “invisibility cloak”. Light also travels in waves, although on a miniscule scale, and scientists have been able to use metamaterials to redirect light waves around objects in the laboratory, hiding the objects from sight. It works because the metamaterials are carefully engineered to bend light in a very specific pattern. Because the light neatly avoids the object it appears to an observer that whatever is hidden by the “cloak” just isn’t there.

By building metamaterials on a much larger scale, the researchers hope to employ the same technique to redirect the waves caused by earthquakes.

This isn’t the first time the search for an invisibility cloak has had unexpected benefits. Waves are everywhere in nature – in the air, the sea and the sky. By using the metamaterials approach, the same team of scientists also hope to deflect tsunamis around vulnerable sea-based structures, such as oilrigs or fragile coastlands. The scientists hope a ring of posts, sunk into the seabed, could act as a metamaterial, redirecting even the power of a tsunami and protecting whatever is sheltered inside.

An illustration of the devastation caused by the 1755 Lisbon Earthquake and Tsunami. Could metamaterials stop this happening in future?

Diamonds may shed light on ancient murder mystery

12,900 years ago, our ancestors may have witnessed one of the most terrifying events imaginable – a direct strike by a massive meteorite.

At this point in our history many large mammal species went extinct, including pygmy mammoths and the sabre-toothed cat (with the excellent scientific name Smilodon fatalis!). Researchers have long argued over what was to blame: climate change, human hunting, or disease. New research by a team from the University of California in the USA now lends support to a fourth compelling possibility – a meteorite strike.

The meteorite hypothesis is supported by the presence of “nanodiamonds” in geological layers of the right age. These microscopic gems require immense temperatures and pressures to form. On Earth they are only ever found near meteorite impact craters.

The nanodiamonds aren’t the only thing in favour of the meteorite claim. Like any good murder investigation, there are multiple lines of evidence pointing to the suspect. The geological period in question, the Pleistocene, also shows evidence of wildfires across North America and dramatic cooling of the climate. The heat released by a meteorite impact would ignite many square miles of forest and grassland, generating large quantities of soot. The force of the impact would also throw dust high into the atmosphere. Combined with smoke from the fires, this would reflect a lot of sunlight back into space, cooling the climate.

Unfortunately, there’s no evidence for a crater of the right age, which would provide much more conclusive evidence.

It is almost impossible to identify the killer in such ancient mysteries. Even the well-studied end of the dinosaurs, sixty five million years ago, remains unclear; with volcanoes in India, meteorites in Mexico, or a combination of the two to blame. The new research into the events of 12,900 year ago presents an interesting argument, but I suspect we’re still a long way from knowing for certain what happened in these dark days before the blossoming of human civilisation.

Diamond hunt, anyone? Image credit Cburnett. Used under GFDL