Geographical - December 2010
w orldwatch n Volcanic clusters explained: A team of University of Oxford scientists has finally explained why the world’s explosive volcanoes are always bunched together in narrow bands, such as those of the so-called Ring of Fire in the Pacific.
‘It has been recognised for almost 50 years that the volcanic arcs form where one oceanic plate sinks beneath another, but while many models of this process have been put forward, none has been able to explain the location, and narrowness, of the volcanic arcs,’ said Professor Philip England, one of the authors of the study, which was published in Nature.
Volcanic eruptions in the Ring of Fire are extremely violent – examples include the 1883 eruption of Krakatoa and that of Toba about 74,000 years ago, which may have almost wiped out the human race. This is caused by the high proportion of water in the molten rock beneath the volcanoes, which turns into explosive superheated steam. The water is liberated when the plates descend into the mantle and lowers the melting point of the surrounding rocks.
Previous theories suggested that this ‘wet melting’ was responsible for the formation of the volcanoes, but this sort of melting takes place over wide areas of the mantle, so it doesn’t explain why the volcanoes tend to be so localised. The Oxford team used mathematical models of heat transport in the regions where plates collide and found that the observed pattern could only be explained if the volcanoes are forming in regions where the mantle is melting in the absence of water. Molten rock rising from these regions blazes a trail that more water-rich magma can follow to the surface, where it erupts to form volcanoes.
n Water insecurity affects billions: A new map of global water security compiled by a team of US researchers suggests that about 80 per cent of the world’s population lives in areas where the freshwater supply is insecure.
he team, led by Charles Vorosmarty of the City College of New York, used a composite index of water threats to both humans and biodiversity, such as scarcity and pollution, in 2,500-square-kilometre squares over the world’s surface. ‘What we’ve done is to take a very dispassionate look at the facts on the ground – what is going on with respect to humanity’s water security and what the infrastructure that has been thrown as this problem does to the natural world,’ Vorosmarty said.
hey found that some of the world’s most threatened rivers are in the developed world, including examples in the USA and western Europe, despite decades of attention to pollution control and investments in environmental protection. Rivers were at least risk in areas where human populations are smallest, such as in the Arctic and in relatively inaccessible parts of the tropics.
ccording to the researchers, conserving water in dams and reservoirs helps to provide security for people, but often damages biodiversity. Instead, governments should combine infrastructure with efforts to safeguard natural resources such as watersheds, wetlands and floodplains.
Elephant damage good for frogs When a herd of African elephants moves through the savannah, it often leaves a trail of destruction in its wake. But according to a new study, this systematic demolition of the environment helps to improve the local species richness. Working in mixed savannah woodlands on the 4,300-hectare Ndarakwai Ranch in northeastern Tanzania, a team of scientists from Georgia Southern University identified areas of high, medium and low elephant damage. They then surveyed these areas for reptiles and amphibians, and compared the results with surveys of a 250-hectare area that had been fenced off to protect it from large herbivores.
The areas with the greatest damage had the highest number of species (nine lizards and nine amphibians), while the fenced area had the lowest (five lizards and three amphibians). The scientists concluded that the difference was down to the so-called ‘ecological engineering’ being carried out by the elephants. ‘Craters and coarse woody debris formed by uprooted and broken trees augmented the number of refuges against predators and dessication,’ they wrote in a paper published in the African Journal of Ecology.
The scientists went on to suggest that further research was needed to determine the full impact of free-ranging elephants on other animals, in particular arboreal species.
HAITI A new study has revealed that January’s devastating earthquake in Haiti didn’t originate from the Enriquillo fault, as previously believed, but from movement on a previously unknown subsurface thrust fault. The movement also didn’t rupture the surface, suggesting that it didn’t release the strain that has built up on faults in the area over the past 20 years, so future surface-rupturing earthquakes are likely.
INDIA The number of people dying from malaria in India has been underestimated by a factor of 13, according to new research. The study suggests that as many as 277,000 deaths are caused each year by the disease; World Health Organization estimates put the number at close to 15,000.
UK The southern boundary of the Cairngorms National Park, the UK’s largest, has been extended to include parts of northern Perthshire. The expansion added 728 square kilometres to the area of the park, which now covers almost six per cent of Scotland.
BENIN The worst flooding in 50 years has killed at least 60 people and ruined or destroyed 55,000 homes in the west African nation of Benin. Two thirds of the country, and at least 680,000 people, has been has affected by rains judged to be twice as heavy as normal.
CHINA China’s first national plan to safeguard biodiversity in 16 years has outlined plans to protect nearly a quarter of the country’s land area and halt the loss of biodiversity in the country by 2020. Based in part on research carried out by the Nature Conservancy, the plan identifies 32 priority areas for conservation.
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