Melting of rocks to produce magmas is governed by the large-scale dynamics produced by those plates and mantle convection, leading to a global correlation of the location of volcanoes and plate boundaries (see figure). Heat loss from Earth’s interior drives mantle convection at speeds of centimeters per year, creating tectonic plates at the surface and recycling those plates into the deep Earth. Melting can be induced by three mechanisms: heating, lowering pressure, or adding a contaminant (e.g., water) to reduce the melting temperature. Will magma stall because of increased viscosity? Or will bubble expansion accelerate magma to the surface in an explosive eruption? The processes that move and store magma are thus fundamental not only to the transfer of mass from the interior to the
#Bubble collapse blast critical drivers#
The competing drivers that force magma to rise and also to resist movement are partly what makes magma movement and eruption so difficult to forecast ( Melnik and Sparks, 2006). These properties evolve over the life cycle of the volcano. Storage and ascent are influenced by the mechanical properties and behavior of the crust, including its ability to deform, flow, or fracture. A loss of volatiles also increases the melt viscosity. Decompression may lead to increased buoyancy due to the formation of bubbles from gas originally dissolved in the melt. Cooling leads to crystallization and increased viscosity. Magma cools because the crust is cooler than the magma, and magma decompresses as it rises. But much of the time, magma stalls and forms reservoirs that later erupt or freeze ( Figure 2.1). At hotspots such as Iceland, Hawaii, and some volcanoes in the western United States, magma can ascend directly from the mantle to the surface.
Magma is buoyant and rises through the crust, sometimes erupting at the surface. The path magma takes to the surface is poorly understood. 2.1 HOW ARE MAGMAS STORED AND TRANSPORTED IN THE CRUST? This chapter summarizes current understanding of how volcanoes work and identifies key questions and research priorities in three areas: (1) processes that move and store magma beneath volcanoes (2) how eruptions begin, evolve, and end and (3) how a volcano erupts. Thus a central challenge to understanding how magma is generated, is stored, ascends, and erupts is to disentangle the unique features of the birth, life, and death of each volcano from the common processes governing their life cycles.
Yet the evolution and eruption of all volcanoes are still governed by the same set of processes intrinsic to the magma and influenced by geologic setting. The interactions between melting, storage, accumulation, eruption, and geologic setting give rise to the great diversity seen in eruptions and volcanic landforms.Įach volcano has its own distinct life cycle, often with multiple episodes of repose, unrest, and eruption. The eruption of magmas creates volcanoes and affects other surface environments such as the hydrosphere and atmosphere. Magma can have a complex history underground.
The silicate melts can then ascend to the surface directly, or accumulate in the crust where their volumes and compositions change as they interact with their surroundings. They are usually conceived by melting in the mantle, and hence their locations are controlled by plate tectonics and mantle convection ( Box 2.1).
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