The layer-forming mechanism we consider relies on the interaction of suspended crystals and/or bubbles with sloping walls and an ambient stratification. Mendenhall and Mason observed layers when a polydisperse suspension, vertically stratified through differential settling, was heated from the side numerical simulations of this phenomena were performed by Hosoi and Dupont. Other plausible layer-forming mechanisms include sidewall cooling (or heating) of stable a density gradient associated with either compositional variations, or sedimenting particles. Time dependent layers may form by the heating from below of a compositional gradient. Double-diffusive convection has been suggested as a possible origin however, in magma chambers the temperature and compositional gradients are not independent, and numerical simulations suggest that no such steady layers may form. While a number of explanations for the existence of layers in solidified magma chambers rely on the presence of convecting layers within the molten chamber, the origin of such layers remains uncertain. While the dynamics of both high and low Reynolds number gravity currents are well understood, the origin of the required large mass of particles is unclear. Particles then sediment out as the current spreads, leaving a deposit that thins with distance from the source. Irvine and subsequently Hodson proposed that layers are the result of deposition from particle-driven gravity currents if a large quantity of crystalline matter generated within the chamber is suddenly released from the top of the chamber, it will sink and spread as a gravity current along the base of the chamber.

The repetition of this process yields a layered deposit. An alternative mechanism relies on episodic crystal settling from a convecting chamber cooled from above when the concentration of crystals becomes sufficiently large, convection is unable to keep them in suspension, leading to a deposition event. One explanation for the existence of layers at the bottom of a magma chamber is the repeated injection of melt : new magma is introduced periodically at the base, each injection leading to the formation of a new layer. A variety of mechanisms have been proposed to explain the formation of layers in solidified magma chambers, but have been difficult to confirm owing to the complexity of the system, the number and indeterminacy of the governing parameters and difficulties in obtaining reliable data. Vesicular layers form near the top of the chamber and usually only a few such layers are observed, with depths of order 20cm.

Vesicular rock layers, those exhibiting high concentrations of volatiles, have been seen in Taiwan and Washington state. In the majority of cases, the composition of the layers varies monotonically with height and the mean density within each layer decreases with height. The individual layers are typically less than one meter deep and the strata may span up to 100m. These layers have been reported in Greenland and South Africa, and their origins are the subject of this letter. At the base of solidified magma chambers, compositionally distinct layers are often observed. Eventually all the magma solidifies and interior motion is suppressed. As the chamber cools, the concentration of crystals increases until a crystal matrix forms and the interior of the magma chamber effectively becomes a porous medium. Crystals, either present when the chamber was initially filled or formed as the chamber cools, and small bubbles of gas or low viscosity liquids (volatiles) may subsequently come to dominate the dynamics of the magma chamber. Through magma differentiation, compositional gradients may develop and render the chamber unstable to compositional convection. The temperature difference across the chamber is diminished by the convective mixing, and viscosity increases as the chamber cools until thermally-driven convection becomes untenable. The system is generally cooled from above so that thermally-driven convection may be present. The chamber is typically filled rapidly with hot magma from the Earth's mantle and subsequently isolated however, reinjections of magma from a source conduit may also arise.

Convective motions and crystal settling have long been thought to play a role in the dynamics of magma chambers. Their geometries vary from roughly spherical to planar, with characteristic dimensions ranging from 100m to 10km. Magma chambers are large reservoirs of molten material contained in solid rock within the earth's mantle.

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