The endogenous growth of pahoehoe lava lobes and morphology of lava-rise edges
Published:January 01, 2009
G. P. L. Walker, 2009. "The endogenous growth of pahoehoe lava lobes and morphology of lava-rise edges", Studies in Volcanology: The Legacy of George Walker, T. Thordarson, S. Self, G. Larsen, S. K. Rowland, Á. Höskuldsson
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Lava-rise structures form by endogenous growth where lava is injected under, and lifts up, its surface crust. They are especially common in pahoehoe where it flows on shallow gradients (.48). Examples are described from the Mauna Loa (Hawaii) 1859 and Xitle (Mexico) 1.5 ka basalt flow-fields, and range from ten to hundreds of metres wide by up to 13 m high. The lobes that host the lava-rise structures were initially thin (≥1 m) and it is estimated that at least 80% of their total volume was emplaced by subcrustal injection. They are bounded by lava-rise edges that are highly distinctive margins with steep banded and striated surfaces (BSS) upon which lava inflation was accommodated. The BSS are emergent surfaces formed where newly injected hot lava cooled and solidified against the air. The surface textures indicate the direction of motion of the lava crust and edges relative to the point of emergence. Some BSS are steep and inwardly dipping reverse faults. Others are divergent-facing pairs of curved surfaces, the walls of lava inflation clefts. Many such clefts commonly transect the main BSS and subdivide them into stacks of lava wedges. A steep foliation defined by the plane of flattening of vesicles also occurs and bulges out into the wedges, attributed to a general expansion of the lava-rise. ‘Lava-rise sutures’ occur between contiguous lava-rises or lava lobes that inflated synchronously against each other. They are common where cross-sections through pahoehoe lavas are seen, such as in flood basalt provinces. In cross-section these features have the aspect of facing stacks of lava wedges, previously interpreted in the Xitle lava and elsewhere to be spiracles (steam-escape structures).
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Studies in Volcanology: The Legacy of George Walker
Professor George Patrick Leonard Walker was one of the fathers of modern quantitative volcanology and arguably the foremost volcanologist of the twentieth century. In his long career, George studied a wide spectrum of volcanological problems and in doing so influenced almost every branch of the field. This volume, which honours his memory and his contributions to the field of volcanology, contains a collection of papers inspired by, and building upon, many of the ideas previously developed by George. Many of the contributors either directly studied under and worked with George, or were profoundly influenced by his ideas. The topics broadly fall under the three themes of lava flows and effusion, explosive volcanism, and volcanoes and their infrastructure.