Volume 1 Issue 8, August 2008

Volume 1 Issue 8

Cratons are ancient continental nuclei that have resisted significant fragmentation for almost two billion years. Yet, many cratons also experience phases of instability in the form of erosion and rejuvenation of their thick lithospheric mantle keels. Melting governed by redox processes, as well as small-scale convection, play a key role in triggering such instability. The image is an artistically enhanced photo of an outcrop of Archaean gneiss, a type of rock that is typical of the crust of Archaean cratons,at Turnavik Island in Labrador.

Cover design by Karen Moore

Editorial

  • Editorial |

    Twice in the month of May 2008 did natural catastrophe strike Asia. Public attention in the wake of destruction offers a chance for better protection in China, Myanmar and elsewhere.

Correspondence

Commentaries

  • Commentary |

    The devastating earthquake in the Chinese province of Sichuan struck an area that was not expected to suffer seismic activity of such magnitude. Yet topographic analyses of the region indicate active deformation, suggesting a way of refining maps of earthquake risk elsewhere.

    • Eric Kirby
    • , Kelin Whipple
    •  & Nathan Harkins
  • Commentary |

    Tropical cyclone Nargis wrought havoc in southern Myanmar, with an estimated death toll well above 100,000. Potential future disasters could be alleviated with currently available forecasting skill and effective disaster mitigation plans.

    • Peter J. Webster

Books and Arts

Research Highlights

News and Views

  • News & Views |

    The Waiho Loop moraine in New Zealand's southern Alps had long been viewed as a southern icon of a recent glacier response to cooling climate, possibly the Younger Dryas cold event. But a closer look has implicated a landslide in this particular glacial advance.

    • David J. A. Evans
  • News & Views |

    In the South Asian lowlands, high population density coincides with dangerous levels of arsenic in groundwater. Maps based on surface geology can help identify regions at risk of arsenic contamination.

    • Alexander van Geen
  • News & Views |

    The ratio of magnesium to calcium in sea water is thought to have influenced the skeletal mineralogy of certain marine calcifiers throughout the Phanerozoic eon. A fresh look at old data suggests that mass extinctions may have also played a role.

    • Justin B. Ries
  • News & Views |

    Almost immediately after all the Earth's continents were amalgamated into the supercontinent Pangaea, rifting began to tear it apart. Subduction of the oceanic region of the Pangaean plate beneath its own continental margin may have been the trigger.

    • Christophe Pascal
  • News & Views |

    Mud volcanoes often exhibit calderas, which are large circular depressions at their summit. Detailed mapping around the Caspian Sea suggests that caldera-forming mud volcanoes are dynamically similar to magmatic volcanoes.

    • Achim J. Kopf

Review

  • Review Article |

    Cratons are ancient continental nuclei that have resisted significant fragmentation for almost two billion years. Yet, many cratons also experience phases of instability in the form of erosion and rejuvenation of their thick lithospheric mantle keels. Melting governed by redox processes as well as small-scale convection play a key role in triggering such instability.

    • Stephen F. Foley

Letters

  • Letter |

    Changes in precipitation extremes under greenhouse warming are commonly assumed to be constrained by the Clausius–Clapeyron relationship, implying an increase in extreme precipitation of 7% per degree of climate warming. An analysis of 99 years of observations along with simulations with a regional climate model show that short-duration precipitation extremes can instead increase in severity twice as fast, by 14% per degree of warming.

    • Geert Lenderink
    •  & Erik van Meijgaard
  • Letter |

    Monsoons are often viewed as planetary-scale sea-breeze circulations, caused by contrasts in the thermal properties between oceans and land surfaces. Numerical simulations suggest that instead feedbacks between large-scale extratropical eddies and the tropical atmospheric overturning circulation are essential for the development of monsoons.

    • Simona Bordoni
    •  & Tapio Schneider
  • Letter |

    The Younger Dryas cold reversal during the last glacial termination is one of the most abrupt climate change events observed in the Northern Hemisphere. Analyses of varved lake sediments from western Germany suggest that storminess in the North Atlantic region increased within a single year at this time, providing a mechanistic link between a decrease in the meridional overturning circulation and western European cooling.

    • Achim Brauer
    • , Gerald H. Haug
    • , Peter Dulski
    • , Daniel M. Sigman
    •  & Jörg F. W. Negendank
  • Letter |

    The Waiho Loop Moraine has been interpreted as evidence for Younger Dryas cooling in southern New Zealand, but recent dating and climatological studies have questioned this idea. A detailed analysis of the sedimentology of the moraine suggests it was formed after a large landslide onto the Franz Josef glacier triggered a glacial surge, independent of climate forcing.

    • D. Santamaria Tovar
    • , J. Shulmeister
    •  & T. R. Davies
  • Letter |

    Changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal mineralogy of marine calcifyers. An investigation of the original skeletal mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the Mg/Ca ratio of the oceans.

    • Wolfgang Kiessling
    • , Martin Aberhan
    •  & Loïc Villier
  • Letter |

    On 13 June 2006, parts of the eastern flank of the Eiger peak in the Swiss Alps collapsed, leading to a major rock fall. The unstable spur on this flank is made up of several blocks that move relative to one another. Instability was initiated by a block at the rear that acted as a wedge and triggered motion of the other blocks.

    • Thierry Oppikofer
    • , Michel Jaboyedoff
    •  & Hans-Rudolf Keusen

Articles

  • Article |

    Arsenic contamination of groundwater resources threatens the health of millions of people worldwide, particularly in the densely populated river deltas of Southeast Asia. Maps of areas at risk of groundwater arsenic concentrations have been produced by combining geological and surface-soil parameters in a logistic regression model. They show that Holocene deltaic and organic-rich surface sediments are key indicators for arsenic risk areas and indicate elevated risks in Sumatra and Myanmar where no groundwater studies exist.

    • Lenny Winkel
    • , Michael Berg
    • , Manouchehr Amini
    • , Stephan J. Hug
    •  & C. Annette Johnson
  • Article |

    Pristine temperate rainforests are known to produce large amounts of bioavailable nitrogen, with only minimal loss. Tracing 15N in volcanic soils of a temperate evergreen rainforest in southern Chile helps to further unravel the retention mechanisms for bioavailable nitrogen in these ecosystems.

    • Dries Huygens
    • , Pascal Boeckx
    • , Pamela Templer
    • , Leandro Paulino
    • , Oswald Van Cleemput
    • , Carlos Oyarzún
    • , Christoph Müller
    •  & Roberto Godoy
  • Article |

    The Earth’s continents amalgamated into the supercontinent Pangaea 320 million years ago. After the supercontinent formed, structural deformation continued, which eventually resulted in the subduction of the ocean margin of Pangaea beneath the continental edge at the other end of the same plate.

    • Gabriel Gutiérrez-Alonso
    • , Javier Fernández-Suárez
    • , Arlo B. Weil
    • , J. Brendan Murphy
    • , R. Damian Nance
    • , Fernando Corfú
    •  & Stephen T. Johnston
  • Article |

    Atmospheric oxygen levels on Earth rose in at least six distinct steps and an examination of the timing of the steps suggests that they coincided with the formation of supercontinents and supermountains. This leads to the hypothesis that increased erosion of these supermountains released large amounts of nutrients to the oceans, stimulating productivity and the release of oxygen to the atmosphere. The subsequent burial of organic carbon along with the mountain sediments would have sustained the increased oxygen levels.

    • Ian H. Campbell
    •  & Charlotte M. Allen

Backstory

  • Backstory |

    Lenny Winkel and colleagues found that strong arm muscles can be required to test South Sumatran groundwater samples for arsenic content.

  • Backstory |

    Balancing their instruments on precarious cliff faces and braving intense media and public attention, Thierry Oppikofer and colleagues monitored the evolution of a rockslide along the eastern flank of the Eiger peak in the Swiss Alps.

  • Backstory |

    Dan Santamaria Tovar, along with advisor Jamie Shulmeister and colleagues, hiked, kayaked and mountain-biked their way through dense New Zealand rainforest in search of the origins of the Waiho Loop moraine.