How much water swept over the Lake Nyos dam during the 1986 gas disaster?

The toxic aerosol of water and carbon dioxide which was released from Lake Nyos in August 1986 passed over the natural dam which confines the lake and devastated the valleys to the north. The gas release generated a wave of water which swept across the lake surface and damaged vegetation on the eastern and southern shore. However, the vegetation to either side of the spillway was undamaged and therefore, despite a recent suggestion to the contrary, any wave of water which passed over the dam could have been no more than a few centimetres high.     

Aleutian magnesian andesites: Melts from subducted Pacific ocean crust

Several diagnostic chemical characteristics of an uncommon Aleutian magma type support a proposed origin that involves a small amount of partial melting of subducted Pacific ocean crust (basalt) consisting mainly of garnet and clinopyroxene (eclogite or garnet websterite). Among the characteristics are high La/Yb ratios and Sr contents and low ratios of radiogenic to non-radiogenic Sr and Pb. The major element composition of the andesites resembles that of hydrous melts in equilibrium with peridotite: a low ratio of total Fe to Mg is distinctive. These disparate observations can be reconciled if large ion lithophile (LIL)- element-rich hydrous melt from the subducted oceanic crust equilibrates with olivine and orthopyroxene in overlying LIL-element-depleted mantle and then erupts without interacting with the island are crust. The compositional dissimilarity of the magnesian andesites and most other andesites from the Aleutian island arc precludes application of this model to island are magmatism in general.     

Unfrozen water contents of submarine permafrost determined by nuclear magnetic resonance

Prior work resulted in the development of techniques to measure the unfrozen water contents in frozen soils by nuclear magnetic resonance (NMR). It has been demonstrated that NMR is a promising new method for the determination of phase composition (the measurement of unfrozen water content as a function of temperature) which circumvents many of the limitations inherent in the adiabatic and isothermal calorimetric techniques. The NMR technique makes it possible, in a non-destructive, non-intrusive way, to explore hysteresis by determining both cooling and warming curves. Corrections are made for dissolved paramagnetic impurities which have the effect of increasing the signal intensity at decreasing temperatures. The results demonstrate that NMR techniques can be effectively utilized both at and below the melting point of ice in frozen soils and that accurate melting points (freezing point depressions) can be determined.     

Estimation of Tigris-Euphrates streamflow from regional paleoenvironmental proxy data

A six thousand year history of streamflow in Mesopotamia is derived from a synthesis of regional paleoenvironmental proxy data. The proxy data are interpreted with consideration to the climatic signals represented in the records and to the temporal resolution of the records. A consideration of modern synoptic climatology suggests the spatial patterns of streamflow-generating precipitation in relation to atmospheric circulation. These patterns provide a framework for the interpretation of streamflow from the regional proxies. Given the nature of the data at hand, only a low frequency signal is reconstructed. Assessment of the role of small scale climatic fluctuations as a forcing function of population dynamics must await the availability of finer resolution environmental data.     

Aleutian tholeiitic and calc-alkaline magma series I: The mafic phenocrysts

Diagnostic mafic silicate assemblages in a continuous spectrum of Aleutian volcanic rocks provide evidence for contrasts in magmatic processes in the Aleutian arc crust. Tectonic segmentation of the arc exerts a primary control on the variable mixing, fractional crystallization and possible assimilation undergone by the magmas. End members of the continuum are termed calc-alkaline (CA) and tholeiitic (TH). CA volcanic rocks (e.g., Buldir and Moffett volcanoes) have low FeO/MgO ratios and contain compositionally diverse phenocryst populations, indicating magma mixing. Their Ni and Cr-rich magnesian olivine and clinopyroxene come from mantle-derived mafic olivine basalts that have mixed with more fractionated magmas at mid-to lower-crustal levels immediately preceding eruption. High-Al amphibole is associated with the mafic end member. In contrast, TH lavas (e.g., Okmok and Westdahl volcanoes) have high FeO/MgO ratios and contain little evidence for mixing. Evolved lavas represent advanced stages of low pressure crystallization from a basaltic magma. These lavas contain groundmass olivine (FO 40–50) and lack Ca-poor pyroxene. Aleutian volcanic rocks with intermediate FeO/MgO ratios are termed transitional tholeiitic (TTH) and calc-alkaline (TCA). TCA magmas are common (e.g., Moffett, Adagdak, Great Sitkin, and Kasatochi volcanoes) and have resulted from mixing of high-Al basalt with more evolved magmas. They contain amphibole (high and low-Al) or orthopyroxene or both and are similar to the Japanese hypersthene-series. TTH magmas (e.g., Okmok and Westdahl) contain orthopyroxene or pigeonite or both, and show some indication of upper crustal mixing. They are mineralogically similar to the Japanese pigeonite-series. High-Al basalt lacks Mg-rich mafic phases and is a derivative magma produced by high pressure fractionation of an olivine tholeiite. The low pressure mineral assemblage of high-Al basalt results from crystallization at higher crustal levels.