Laguna Del Maule (volcano)

Laguna del Maule is a volcanic field in the Andes mountain range of Chile, close to, and partly overlapping, the Argentina–Chile border. The bulk of the volcanic field is in the Talca Province of Chile's Maule Region. It is a segment of the Southern Volcanic Zone, part of the Andean Volcanic Belt. The volcanic field covers an area of and features at least 130 volcanic vents. Volcanic activity has generated cones, lava domes, lava coulees and lava flows, which surround the Laguna del Maule lake. The field gets its name from the lake, which is also the source of the Maule River.

The field's volcanic activity began 1.5million years ago during the Pleistocene epoch; such activity has continued into the postglacial and Holocene epoch after glaciers retreated from the area. Postglacial volcanic activity has included eruptions with simultaneous explosive and effusive components, as well as eruptions with only one component. In the postglacial era, volcanic activity has increased at Laguna del Maule, with the volcanic field rapidly inflating during the Holocene. Three major caldera-forming eruptions took place in the volcanic field prior to the last glacial period. The most recent eruptions in the volcanic field took place , and ago and generated lava flows; today geothermal phenomena occur at Laguna del Maule. Volcanic rocks in the field include basalt, andesite, dacite and rhyolite; the latter along with rhyodacite makes up most of the Holocene rocks. In pre-Columbian times, the field was a regionally important source of obsidian.

Between 2004 and 2007, ground inflation began in the volcanic field, indicating the intrusion of a sill beneath it. The rate of inflation is faster than those measured on other inflating volcanoes such as Uturunku in Bolivia and Yellowstone Caldera in the United States and has been accompanied by anomalies in soil gas emission and seismic activity. This pattern has created concern about the potential for impending large-scale eruptive activity.

Geography and structure

The Laguna del Maule volcanic field straddles the Chilean–Argentine frontier; most of the complex lies on the Chilean side. The locality belongs to the Maule Region, of Talca Province in the Andes mountain range; it is close to the confluence of the Maule and Campanario rivers in the Maule valley. The city of Talca lies about west. The Argentine section of the field is in the Mendoza and Neuquén provinces, and the city of Malargüe is located about east from the volcanic field. The seasonal passes through the northern part of the volcanic field. The Paso Pehuenche mountain pass few kilometres northeast of the lake connects Argentina and Chile; the Chilean customs are at the outlet of the lake. Tourists and fishermen come to the lake during summer, and the crew of the Laguna del Maule dam remains there year-round. Otherwise, the region is sparsely inhabited and economic activity is limited to oil prospecting, pastures and tourism; the closest towns are La Mina and Los Cipreses over northwest of Laguna del Maule.

The Laguna del Maule volcanic field covers a surface area of and contains at least 130volcanic vents including cones, lava domes, lava flows, and shield volcanoes; 36silicic coulees and lava domes surround the lake. Over of the field is covered by these volcanic rocks. The volcanic field lies at an average height of , and some summits around Laguna del Maule reach altitudes of . Volcanic ash and pumice produced by the eruptions has been found over away in Argentina. A number of Quaternary volcanic systems of various ages surround Laguna del Maule lake, including about 14 shield volcanoes and stratovolcanoes that have been degraded by glaciation. The topography in the area is often steep.

Among the structures in the volcanic field, the Domo del Maule lava dome is of rhyolitic composition and generated a lava flow to the north that dammed the Laguna del Maule. This lava flow is joined by other lava flows from the , a small cone in the southwest sector of the volcanic field; the lavas of this cone are andesitic and basaltic. is a large lava flow of acidic rocks that is long in the northern sector of the volcanic field, close to the outlet of Laguna del Maule. It consists of two lobes with a volume of about and contains obsidian and vitrophyre. Crystals within the flow reflect the sunlight. The well-preserved lava flow is in the extreme southwest sector of the volcanic field and originates at a tuff cone. This lava flow is thick, varying from to in length, and is about wide. The Barrancas centre has a volume of and reaches an elevation of .

Past glaciation of this part of the Andes left traces in adjacent valleys, such as their U-shaped or trench-shaped outline. The older volcanics of Laguna del Maule have been disproportionately eroded by glacial action. Slopes around Laguna del Maule lake are covered by colluvium including talus.

The Laguna del Maule lake lies on the crest of the Andes, within a depression with a diameter of . The lake has a depth of and covers a surface of ; the surface is at an altitude of . The name of the volcanic field comes from the lake, which contains several islets. On the lakefloor are slump scars, pits that may be pockmarks, and a basin in the northern lake sector that may be the crater of an early Holocene Plinian eruption. Terraces around the lake indicate that water levels have fluctuated in the past; an eruption dated between and ago dammed the lake higher than its present level. When the dam broke 9,400years ago, a lake outburst flood occurred that released of water and left traces, such as scour, in the down-valley gorge. Benches and beach bars developed on the lake, which has left a shoreline around Laguna del Maule lake. The lake is regulated by a dam at the outlet; it was built in 1950 and completed in 1957 and caused a slight expansion of the lake's area. Laguna del Maule is Chile's fourth-largest reservoir with a capacity of . Additionally, tephra fallout such as from the 1932 Quizapu eruption has impacted the lake through the Holocene and affected life in the lake waters.

Besides Laguna del Maule, other lakes in the field are Laguna El Piojo on the Chilean side in the southwest sector of the field, Laguna Cari Launa on the Chilean side in the northeastern sector of the field, and Laguna Fea in the south at elevation and Laguna Negra lake both on the Argentine side. Laguna Fea is dammed by a pumice dam and currently lacks an outlet. The Laguna Sin Salida ("lake without exit"; so named because it lacks a river running out of it) is in the northeastern sector of the volcanic field and it formed within a glacial cirque. The Andean drainage divide runs across the volcanic field; most of it lies west of the divide and drains into the Maule River, partially through its tributary Melado. The Maule river originates in the field and the Pehuenche and Barrancas Rivers have their headwaters in the volcanic field as well.

Geology

Subduction of the eastern part of the Nazca plate beneath the western margin of the South American plate occurs at a rate of about . This subduction process is responsible for growth of the Chilean Andes, and volcanic and geothermal manifestations such as the 1960 Valdivia earthquake and the 2010 Chile earthquake, as well as Laguna del Maule, which formed behind the volcanic arc.

A phase of strong volcanic activity began in the Andes 25million years ago, probably due to increased convergence rates of the Nazca and South America plates over the past 28million years. It is likely that this phase has persisted without interruption until today.

The subduction of the Nazca plate beneath the South American plate has formed a volcanic arc about long, which is subdivided into several segments distinguished by varying angles of subduction. The part of the volcanic belt named the Southern Volcanic Zone contains at least 60volcanoes with historical activity and three major caldera systems. Major volcanoes of the Southern Volcanic Zone include from north to south: Maipo, Cerro Azul, Calabozos, Tatara-San Pedro, Laguna del Maule, Antuco, Villarrica, Puyehue-Cordón Caulle, Osorno, and Chaitén. Laguna del Maule is located within a segment known as the Transitional Southern Volcanic Zone, west of the Peru–Chile Trench and behind the main arc. Volcanoes in this segment are typically located on basement blocks that have been uplifted between extensional basins.

In the area of Laguna del Maule, the subducting Nazca plate reaches a depth of and is 37million years old. During the Late Miocene, the convergence rate was higher than today and the Malargüe fold belt formed east of the main chain in response. The Moho is found at depths of beneath the volcanic field.

Local

The Campanario Formation is 15.3 to 7million years old and forms much of the basement in the Laguna del Maule area; this geological formation contains andesitic-dacitic ignimbrites and tuffs with later dacitic dykes that were emplaced years ago. An older unit, of Jurassic–Cretaceous age, crops out northwest of the volcanic field. Other units include an Oligocene–Miocene group of lacustrine and fluvial formations named Cura-Mallín, and another intermediary formation named Trapa-Trapa, which is of volcanic origin and between 19and 10million years old. Remnants of Quaternary ignimbrites and Pliocene

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