June 2008 Geology and GSA Today media highlights

Mantle convection and the recent evolution of the Colorado Plateau and the Rio Grande Rift valley

Robert Moucha et al., CP 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada. Pages 439-442.

There is a longstanding debate among geologists about the origin of the Colorado Plateau's unusually high elevation. Using new high-resolution seismic images of Earth's interior structure, Moucha et al. demonstrate through numerical modeling that the Colorado Plateau is overlying a hot mantle plume that drives some of this unusually high elevation. This new view of the deep dynamics and structure below the southwestern United States also has important implications for some of the geologically recent volcanic activity in New Mexico, as well as for the rifting dynamics of the nearby Rio Grande Rift. Understanding the rifting dynamics in this area is important for evaluating the seismic hazard that the Rio Grande Rift may pose.

Iceberg scours along the southern U.S. Atlantic margin

Jenna C. Hill et al., Center for Marine and Wetland Studies, Coastal Carolina University, P.O. Box 261954, Conway, South Carolina 29528-6054, USA. Pages 447-450.

Hill et al. present high-resolution swath bathymetry data collected offshore of South Carolina as part of the National Oceanic and Atmospheric Administration's Ocean Explorations program in 2006 and 2007 to show evidence of extensive iceberg scouring along the upper slope of the continental margin (170–220 m water depth). The seafloor morphology in this region is characterized by numerous west-southwest–oriented grooves. These features are flanked by piles of sediment and boulders along each side, suggestive of iceberg keels plowing into the seafloor. The grooves often terminate in circular pits ringed by ridges several meters high, where icebergs came to rest on the seafloor. The location and orientation of the keel marks suggest icebergs were entrained in a southwestward-flowing coastal current. Currently, the warm waters of the rapid, northeastward-flowing Gulf Stream bathe the upper slope across the region. An offshore shift in the Gulf Stream axis during a period of lowered sea level may have allowed glacially fed coastal currents to penetrate farther south, transporting icebergs to this portion of the margin. This is the first evidence of iceberg transport this far south along the U.S. Atlantic margin.

Climate-induced variations of geyser periodicity in Yellowstone National Park, USA

Shaul Hurwitz et al., U.S. Geological Survey, MS 439, 345 Middlefield Road, Menlo Park, California 94025, USA. Pages 451-454.

By statistically analyzing the variations in intervals between geyser eruptions, Hurwitz et al. demonstrate that several geysers in Yellowstone's Upper Geyser Basin respond to long-term precipitation trends and to the seasonal hydrologic cycle.

Coralline red algae as high-resolution climate recorders