AGU journal highlights -- Aug. 1, 2007

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030335, 2007

3. An alternative mechanism for recent volcanism on Mars

High-resolution images of Martian volcanoes have revealed areas that show signs of recent lava flow. The youngest of these are about 2 million years old, as evidenced by the lack of impact craters on the flows. These flows are confined to Tharsis and Elysium, old volcanoes which exhibit a thickened crust compared to surrounding areas. Previous studies explain these recent volcanics by hypothesizing that strong mantle plumes arising from the core-mantle boundary fuel the melts, but the existence and sustainment of these plumes during the last few billion years is uncertain under Martian conditions. Schumacher and Breuer propose a different hypothesis whereby the crust insulates the mantle, causing the mantle to cool slower than previously expected. Through model simulations, they discover that a locally thickened crust with a reduced thermal conductivity and enriched in radioactive heat sources in comparison to the mantle could generate temperature variations in the upper mantle. These variations could form partial melts below this crustal lid, which, being more buoyant than surrounding material, could ooze out onto the Martian surface.

Title: An alternative mechanism for recent volcanism on Mars

Authors: Sandra Schumacher: Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany;

Doris Breuer: Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt, Berlin-Adlershof, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030083, 2007

4. Estimating tropical cyclone numbers in the North Atlantic before satellites

Trends in hurricane occurrence over the North Atlantic are difficult to determine because hurricanes likely went undetected before satellite observations were available. To estimate the occurrence of these undetected hurricanes, Chang and Guo examine ship track records before and during the satellite era. They map satellite-derived cyclone tracks from 1976 to 2005 against ship tracks from the same time period to determine the probability that ships recorded wind speeds high enough to detect a tropical cyclone. Then, they compute the probability that ships that sailed between 1900 and 1965 would have made observations of similar high wind speeds, if tropical cyclones from the satellite era had been present at the same rate during earlier years. From this, the authors find which storm tracks were too far away from ships to be detected. They determine that the number of tropical cyclones not making landfall over any continent or island likely was underestimated by 1 or less per year after World War I. Thus, their results suggest that the characteristics of North Atlantic tropical cyclone track statistics might have changed during recent decades.

Title: Is the number of North Atlantic tropical cyclones significantly underestimated prior to the availability of satellite observations"