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Continental fl ood basalt provinces are the subaerial expression of large igneous province volcanism. The emplacement of a continental fl ood basalt is an exceptional volcanic event in the geological history of our planet with the potential to directly impact Earth’s atmosphere and environment. Large igneous province volcanism appears to have occurred episodically every 10‐30 m.y. through most of Earth history. Most continental fl ood basalt provinces appear to have formed within 1‐3 m.y., and within this period, one or more pulses of great magma production and lava eruption took place. These pulses may have lasted from 1 m.y. to as little as a few hundred thousand years. Within these pulses, tens to hundreds of volumetrically large eruptions took place, each producing 10 3 ‐10 4 km 3 of predominantly pāhoehoe lava and releasing unprecedented amounts of volcanic gases and ash into the atmosphere. The majority of magmatic gas species released had the potential to alter climate and/or atmospheric composition, in particular during violent explosive phases at the eruptive vents when volcanic gases were lofted into the stratosphere. Aside from the direct release of magmatic gases, magma-sediment interactions featured in some continental fl ood basalt provinces could have released additional carbon, sulfur, and halogen-bearing species into the atmosphere. Despite their potential importance, given the different nature of the country rock associated with each continental fl ood basalt province, it is diffi cult to make generalizations about these emissions from one province to another. The coincidence of continental fl ood basalt volcanism with periods of major biotic change is well substantiated, but the actual mechanisms by which

Repetitive and violent Vulcanian explosion sequences are common hazards at many volcanoes. Statistical analyses of such sequences form the basis of forecasting models and reveal underlying explosive processes. However, no single statistical model describes interexplosion repose intervals in Vulcanian systems. Soufrière Hills, Montserrat, is best described by a log-logistic model, while Sakurajima, Japan, shows a transition from a log-logistic to a Weibull model as activity intensifies. Anak Krakatau, Indonesia, displays two failure modes on different time scales, both described by Weibull distributions. At the Kameni Islands, Santorini, Greece, model-fitting parameters vary between eruption cycles. Rates of magma rise and pressurization may be the most important controls in determining the statistical distribution of repose intervals in Vulcanian systems. © 2007 The Geological Society of America.

Hot volcanic vents promote the thermal fixation of atmospheric N 2 into biologically available forms. The importance of this process for the global nitrogen cycle is poorly understood. At Masaya volcano, Nicaragua, NO and NO2 are intimately associated with volcanic aerosol, such that NOx levels reach as much as an order of magnitude above local background. In-plume HNO 3 concentrations are elevated above background to an even greater extent (≤50 μmol·m-3). We estimate the production efficiency of fixed nitrogen at hot vents to be ∼3 × 10-8 mol·J-1, implying present-day global production of ∼109 mol of fixed N per year. Although conversion efficiency would have been lower in a preoxygenated atmosphere, we suggest that subaerial volcanoes potentially constituted an important source of fixed nitrogen in the early Earth, producing as much as ∼1011 mol·yr-1 of fixed N during major episodes of volcanism. These fluxes are comparable to estimated nitrogen-fixation rates in the prebiotic Earth from other major sources such as bolide impacts and thunderstorm and volcanic lightning. © 2004 Geological Society of America.