1. Wochenbericht POS 522 [POS522]

10/04/18 to 15/04/1

2. Wochenbericht POS513

(15/05/17 to 21/05/17

Cyclic volcanism at convergent margins: linked to aarth orbital parameters or climate changes?

EGU2010-13373 The frequency of volcanic activity varies on a wide rangeof spatial and temporal scales, from <1 yr. periodicities in single volcanic systems to periodicities of 106 yrs. in global volcanism. The causes of these periodicities are poorly understood although the long-term global variations are likely linked to plate-tectonic processes. Here we present evidence for temporal changes in eruption frequencies at an intermediate time scale (104 yrs.) using the Pleistocene to recent records of widespread tephras of sub-Plinian to Plinian, and occasionally co-ignimbrite origin, along the Pacific Ring of Fire, which accounts for about half of the global length of 44,000 km of active subduction. Eruptions at arc volcanoes tend to be highly explosive and the well-preserved tephra records from the ocean floor can be assumed to be representative of how eruption frequencies varied with time. Volcanic activity along the Pacific Ring of Fire evolved through alternating phases of high and low frequency; although there is modulation by local and regional geologic conditions, these variations have a statistically significant periodicity of 43 ka that overlaps with the temporal variation in the obliquity of the Earth’s rotation axis, an orbital parameter that also exerts a strong control on global climate changes. This may suggest that the frequency of volcanic activity is controlled by effects of global climate changes. However, the strongest physical effects of climate change occur at 100 ka periods which are not seen in the volcanic record. We therefore propose that the frequency of volcanic activity is directly influenced by minute changes in the tidal forces induced by the varying obliquity resulting in long-period gravitational disturbances acting on the upper mantle

The 12.4 ka Upper Apoyeque Tephra, Nicaragua: stratigraphy, dispersal, composition, magma reservoir conditions and trigger of the plinian eruption

Highly-explosive plinian eruptions belong to the most devastating phenomena of volcanic activity. Upper Apoyeque Tephra (UAq), erupted in close vicinity of the Managua city region in west-central Nicaragua with two million inhabitants, was formed by a rhyodacitic plinian eruption at 12.4 ka BP. The fallout tephra was dispersed from a progressively rising plinian eruption column that became exposed to different wind speeds and directions at different heights in the stratosphere, leading to an asymmetric tephra fan with different facies in the western and southern sector. Tephra dispersal data integrated with geochemical compositions of lava flows in the area facilitate to delimit the source vent to the south of Chiltepe Peninsula. UAq, Lower Apoyeque Tephra, Apoyeque Ignimbrite, and two lithic clasts in San Isidro Tephra together form a trend distinct from that of the younger tephras and lavas at Chiltepe Volcanic Complex in a TiO2 versus K2O diagram, compositionally precluding a genetic relationship of UAq with the present-day Apoyeque Volcano. Apoyeque Volcano in its present shape did not exist at the time of the UAq eruption. The surface expression of the UAq vent is now obscured by younger eruption products and lake water. Pressure-temperature constraints based on mineral-melt equilibria indicate at least two magma storage levels. Clinopyroxenes crystallised in a deep crustal reservoir at ~24 km depth as inferred from clinopyroxene-melt inclusion pairs. Chemical disequilibrium between clinopyroxenes and matrix glasses indicate rapid magma ascent to the shallower reservoir at ~5.4 km depth, where magnesiohornblendes and plagioclase fractionated at a temperature of ~830°C. Water concentrations ranged at ~5.5 wt. % as derived from congruent results of amphibole and plagioclase-melt hygrometry. The eruption was triggered through injection of a hotter, more primitive melt into a water-supersaturated reservoir

POS522 Cruise report

R.V. Poseidon cruise no. 522 Dates, Ports: 10.04.2018 (Catania, Italy) – 29.04.2018 (Malaga, Spain) Research subject: Tephrostratigraphy of tsunami-related deposits at Stromboli Chief Scientist: Dr. Armin Freundt, GEOMAR, Kiel Number of Scientists: 11 Project: Stromboli tsunami

POS 513 [POS513] Cruise Report

Dates, Ports: 09.05.2017 (Heraklion, Crete) – 24.05.2017 (Heraklion, Crete) Research subject: Tephrostratigraphy along the Aegean arc Chief Scientist: Dr. Armin Freundt, GEOMAR, Kiel Number of Scientists: 11 Project: Aegean Tephra