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Laacher See volcano erupted about 12,900 years ago, resulting in a tephra blanket widely dispersed in central Europe. The eruption tapped a chemically and mineralogically strongly zoned phonolitic magma reservoir. In order to better constrain the pre-eruptive storage of that magma, hydrothermal phase equilibria experiments have been performed on a powdered sample from the highly evolved phonolite of the Lower Laacher See Tephra (LLST). Experiments were run at water pressures of 75–175 MPa and temperatures of 725–800 °C. Stability fields of sanidine and amphibole, the most common crystal phases in LLST, suggest that the magma last equilibrated at temperatures of 750–760 °C and pressures of 115–145 MPa. Those conditions suggest the magma should have contained between 5 and 6 wt.% water, which agrees well with water contents of 5.7 wt.% found in glass inclusions. That agreement, along with the observation that Cl and S vary with the composition of the inclusions, suggest that the Laacher See magma was saturated at depth with a water-rich fluid, and thus was stored at pressures near those estimated from our experiments. Such pressures roughly correspond to depths of 5–6 km. Clinopyroxene and plagioclase did not occur in the experimental runs, although present in the natural pumice sample. It seems likely that these phases are not inherent to the LLST. They were formed in other parts of the chemically stratified column and later redistributed. A recalculation of the magma density, together with a new estimate of the temperature and pressure range suggests a steep density gradient and a thin withdrawal layer, which is typical for volatile-enriched magma bodies and confirms earlier models of convective fractionation in the Laacher See magma reservoir.

The relation of eruptive intensity with magma composition and viscosity has been investigated for Mount St Helens where eruptive activity has ranged from basaltic lava flows to dacitic Plinian eruptions. The Plinian eruptions have varied in eruptive intensity from 10 6 to 10 8 kg/s, yet all erupted dacitic magma. These dacites, however, differ greatly in temperature, water content, and crystallinity, and thus magma viscosity varies by two orders of magnitude. The variation in viscosity is correlated inversely with intensity. In addition, more mafic magmas erupted at lower intensities, showing that the wide range in eruptive behavior is linked to magma composition. Changes in composition result mainly from mixing of basaltic and dacitic magmas and occur in cycles. The rate of change during a cycle depends upon the length of the preceding repose period and the flux of basalt to the reservoir. -from Authors

Variations in eruption column height, magma discharge (intensity), and geochemistry have been documented for the plinian phase of the Bishop Tuff eruption from the Long Valley caldera, California. Although exposures of the complete Bishop fall deposit are sparse, their widespread relationships, knowledge of the plinian vent location, and a reasonable estimate of the main dispersal axis allow for the construction of minimum clast isopleths. Column height and intensity are estimated to have increased from 23 km and 7 × 107 kg s-1 to a peak of 45 km and 7.5 × 108 kg s-1 at the end of the plinian phase. Variations in geochemistry of the plinian deposit reveal complex magma withdrawal processes during the Bishop plinian phase. Based on the physical volcanology and compositional variations in the plinian deposit, a model is proposed for the temporal progression of magma withdrawal during the plinian phase. -from Authors

Peak eruption column heights for the B1, B2, B3 and B4 units of the May 18, 1980 fall deposit from Mount St. Helens have been determined from pumice and lithic clast sizes and models of tephra dispersal. Column heights determined from the fall deposit agree well with those determined by radar measurements. B1 and B2 units were derived from plinian activity between 0900 and about 1215 hrs. B3 was formed by fallout of tephra from plumes that rose off pyroclastic flows from about 1215 to 1630 hrs. A brief return to plinian activity between 1630 and 1715 hrs was marked by a maximum in column height (19 km) during deposition of B4. Variations in magma discharge during the eruption have been reconstructed from modelling of column height during plinian discharge and mass-balance calculations based on the volume of pyroclastic flows and coignimbrite ash. Peak magma discharge occurred during the period 1215-1630 hrs, when pyroclastic flows were generated by collapse of low fountains through the crater breach. Pyroclastic flow deposits and the widely dispersed co-ignimbrite ash account for 77% of the total erupted mass, with only 23% derived from plinian discharge. A shift in eruptive style at noon on May 18 may have been associated with increase in magma discharge and the eruption of silicic andesite mingled with the dominant mafic dacite. Increasing abundance of the silicic andesite during the period of highest magma discharge is consistent with the draw-up and tapping of deeper levels in the magma reservoir, as predicted by theoretical models of magma withdrawal. Return to plinian activity late in the afternoon, when magma discharge decreased, is consistent with theoretical predictions of eruption column behavior. The dominant generation of pyroclastic flows during the May 18 eruption can be attributed to the low bulk volatile content of the magma and the increasing magma discharge that resulted in the transition from a stable, convective eruption column to a collapsing on

The purpose of this study is to determine the presence and habitat suitability for the Indiana Bat and Gray Bat for portions of the lower 6.6 miles (10.6 km) of McKee Creek; McGee Creek Drainage and Levee District, Pike Co., Ill. Three channel cutoffs are scheduled to be constructed to straiten McKee Creek before it's destination into the Illinois River, in an effort to provide better drainage in the surrounding heavily agriculturalized area. This study involves mist netting for bats inside each of the proposed cutoffs, between each cutoff and collecting localities immediately upstream and immediately downstream of the study area. A number of data were collected in determining habitat suitability, such as characterization of riparian habitat, description of the stream and data generated from live trapping bats. It is not the intention or duty of this report to comment on the possible effects on the local bat fauna by altering the course of McKee Creek. Bat fauna will be discussed in relation to all species captured, however, major emphasis will be placed on the endangered species, Myotis sodalis, captured during this study.