August GEOLOGY and GSA TODAY Media Highlights

Volcanic eruptive activity is strongly dependent on the style of magma degassing. Remote spectroscopic measurements of volcanic gas composition at Kilauea volcano, in Hawaii, by Edmonds and Gerlach have revealed aspects of shallow volcanic degassing processes. Bubbles in magma change in composition as they ascend a volcanic conduit, owing to decompression, changes in magma and vapor composition, and the degree of vapor segregation and loss from the host melt (open- or closed-system degassing). Open-path Fourier transform infrared spectroscopy measurements of the volcanic gases, using incandescent lava vents as infrared sources, have revealed changes in volcanic gas composition over time that correspond to distinct degassing regimes. Gas piston events are associated with the emission of CO2-rich gases (up to 70 mol%) and are caused by the accumulation of vapor at depths of 400–900 meters beneath Pu'u 'Ō'ō. Lava spattering is associated with the bursting of H2O-rich bubbles, which are formed by open-system degassing in the shallow (<150 meters) conduit. Large bubbles ascend through the melt, harvesting smaller bubbles and accelerating, bursting at the surface, causing spatter. Static gas accumulation and dynamic bubble coalescence are both manifestations of vapor segregation in low viscosity basaltic melts.

Active thrusting offshore Mount Lebanon: Source of the tsunamigenic A.D. 551 Beirut-Tripoli earthquake
Ata Elias et al., IPGP, Tectonique, Boite 89, 4 Place Jussieu, Paris 75252, Cedex 05, France. Pages 755-758.

On 9 July 9 A.D. 551, a large earthquake, followed by a tsunami, destroyed most of the coastal cities of Phoenicia (modern-day Lebanon). This was one of the most devastating historical earthquakes in the eastern Mediterranean. New marine geophysical data help unveil its source: the rupture of a previously unknown, albeit major, submarine fault, offshore of Mount Lebanon. This active fault is also responsible for the build-up of the Mount Lebanon range that towers around 3100 meters above sea level. Sets of uplifted shorelines along the Lebanese coast, attributed to repeated earthquakes on this fault, hint to a 1500–1750 year recurrence period for similar A.D. 551-sized earthquakes. The next destructive, tsunamigenic earthquake may occur soon.

Geophysical insights into the Transition fault debate: Propagating strike slip in response to stalling Yakutat block subduction in the Gulf of Alaska
Sean P.S. Gulick et al., University of Texas, Jackson School of Geosciences, Institute for Geophysics, J.J. Pickle Research Campus, 10100 Burnet Road, Mail Code R2200, Austin, TX 78758, USA. Pages 763-766.