Abstract
Abstract. Late Quaternary volcanic basins are active landscapes from which detailed archives of past climate and seismic and volcanic activity can be obtained. A multidisciplinary study performed on a transect of sediment cores was used to reconstruct the depositional evolution of the high-elevation Laguna del Maule (LdM) (36∘ S, 2180 m a.s.l., Chilean Andes). The recovered 5 m composite sediment sequence includes two thick turbidite units (LT1 and LT2) and numerous tephra layers (23 ash and 6 lapilli). We produced an age model based on nine new 14C AMS dates, existing 210Pb and 137Cs data, and the Quizapú ash horizon (1932 CE). According to this age model, the relatively drier Early Holocene was followed by a phase of increased productivity during the mid-Holocene and higher lake levels after 4.0 ka cal BP. Major hydroclimate transitions occurred at ca. 11, 8.0, 4.0 and 0.5 ka cal BP. Decreased summer insolation and winter precipitation due to a southward shift in the southern westerly winds and a strengthened Pacific Subtropical High could explain Early Holocene lower lake levels. Increased biological productivity during the mid-Holocene (∼8.0 to 6.0 ka cal BP) is coeval with a warm–dry phase described for much of southern South America. Periods of higher lake productivity are synchronous to a higher frequency of volcanic events. During the Late Holocene, the tephra layers show compositional changes suggesting a transition from silica-rich to silica-poor magmas at around 4.0 ka cal BP. This transition was synchronous with increased variability of sedimentary facies and geochemical proxies, indicating higher lake levels and increased moisture at LdM after 4.0 ka cal BP, most likely caused by the inception of current El Niño–Southern Oscillation and Pacific Decadal Oscillation (ENSO–PDO) dynamics in central Chile.
Highlights
The Andes of central Chile are prone to drought, and future scenarios of global warming show them becoming drier as winter droughts are more recurrent (Falvey and Garreaud, 2009; Stocker et al, 2013; Boisier et al, 2016)
The cores were linked to the seismic data with a depth–time conversion, assuming an acoustic velocity of 1500 m s−1 and using the density values and the P-wave velocity measured in the cores with a Geotek Multi-Sensor Core Logger (MSCL)
The base of the core in site 1 is composed of coarse breccia with angular centimeter-long volcanic clasts in a volcanic matrix that likely represents brecciated volcanic facies emplaced in the distal areas of the lake
Summary
The Andes of central Chile (or southern Central Andes; SCA hereafter) are prone to drought, and future scenarios of global warming show them becoming drier as winter droughts are more recurrent (Falvey and Garreaud, 2009; Stocker et al, 2013; Boisier et al, 2016). With one major eruptive event in the last 200 a from the Quizapú Volcano (Plinian eruption with a volcanic explosivity index (VEI) = 5; Fontijn et al, 2014), underlines that this is a regional hazard for the society and the economy of central Chile (Hildreth and Drake, 1992). The LdM volcanic field has shown extremely high rates of deformation (Andersen et al, 2012; Feigl et al, 2014; Singer et al, 2018; Wespestad et al, 2019) that can be interpreted as a response to shallow magma intrusion, indicating intensified volcanic activity and hazard (Fig. 1)
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