Eruptive history of the Krakatau volcanic complex, Indonesia

[EN] The 1883 eruption of Krakatau is one of the best known volcanic events in the world, although it was not the largest, nor the deadliest of known eruptions. However, the eruption happened in a critical moment (just after the first global telegraph network was established) and in a strategic place (the Sunda Straits were a naval traffic hot spot at that time). The lecture will explore these events in some detail before presenting an outline on ongoing multidisciplinary efforts to unravel the past and present day plumbing systems of the 1883 eruption and that of the active Anak Krakatau cone. A mid- and a lower-crustal magma storage level exist beneath the volcano, placing significant emphasis on magma-crust interaction in the uppermost, sediment-rich crust. This final aspect shares similarities with the 2011/2012 El Hierro eruption, highlighting the relevance of the interaction between ascending magmas and marine deposits that oceanic magmas have to pass. At Krakatau, shallow-level crustal contamination offers a possible explanation for the explosive nature of the 1883 eruption and also for those of the presently active Anak Krakatau edifice and helps constrain location, style and processes of subvolcanic magma storage.

Analisi geochimica delle acque iperacide del lago craterico del vulcano Kawah Ijen (Java, Indonesia).

I laghi vulcanici sono corpi idrici che si posizionano all’interno di crateri originatisi da eruzioni idrotermali, idrovulcaniche o magmatiche. Dato il particolare ambiente di formazione di questi bacini, le condizioni fisico-chimiche delle loro acque riflettono l’influenza dei diversi “input” vulcanici quali gas e fluidi che risultano dall’interazione tra le acque sotterranee e i fluidi rilasciati da un corpo magmatico in profondità. Il presente lavoro consiste nella caratterizzazione geochimica delle acque del lago craterico del Kawah Ijen e nella definizione dei principali processi che la controllano, come i processi di diluizione, degassamento e precipitazione di fasi minerali. Tale definizione è la base conoscitiva necessaria per una più realistica interpretazione delle eventuali variazioni geochimiche spazio-temporali

Depositional modes and lake-level variability at Lake Towuti, Indonesia, during the past ~29 kyr BP

Lake Towuti (2.5°S, 121.5°E) is a long-lived, tectonic lake located on the Island of Sulawesi, Indonesia, and in the center of the Indo-Pacific warm pool (IPWP). Lake Towuti is connected with upstream lakes Matano and Mahalona through the Mahalona River, which constitutes the largest inlet to the lake. The Mahalona River Delta is prograding into Lake Towuti’s deep northern basin thus exerting significant control on depositional processes in the basin. We combine high-resolution seismic reflection and sedimentological datasets from a 19.8-m-long sediment piston core from the distal edge of this delta to characterize fluctuations in deltaic sedimentation during the past ~29 kyr BP and their relation to climatic change. Our datasets reveal that, in the present, sedimentation is strongly influenced by deposition of laterally transported sediments sourced from the Mahalona River Delta. Variations in the amount of laterally transported sediments, as expressed by coarse fraction amounts in pelagic muds and turbidite recurrence rates and cumulative thicknesses, are primarily a function of lake-level induced delta slope instability and delta progradation into the basin. We infer lowest lake-levels between ~29 and 16, a gradual lake level rise between ~16 and 11, and high lake-levels between ~11 and 0 kyr BP. Periods of highest turbidite deposition, ~26 to 24 and ~18 to 16 kyr BP coincide with Heinrich events 2 and 1, respectively. Our lake-level reconstruction therefore supports previous observations based on geochemical hydroclimate proxies of a very dry last glacial and a wet Holocene in the region, and provides new evidence of millennial-scale variations in moisture balance in the IPWP.