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

On-shore and off-shore tephrostratigraphy: Mass budgets, Time series, and Implications for geological processes

This cumulative work summarizes seven manuscripts published between 2007 and 2012. These studies use marine and on-shore tephrostratigraphy as a tool to quantify and identify the timing, extent, and causes of geological processes taken place at subductions zones. In many subduction-related regions on Earth, highly explosive plinian volcanic eruptions generate buoyant, tephra bearing eruption columns capable of penetrating up to 40 km into the stratosphere, where they reach a neutral level of buoyancy and spread laterally. Such eruption clouds drift with the prevailing wind over nearby oceans, gradually dropping their ash load over areas that sometimes can be larger than 106 km2. The resulting ash layers are best preserved in non-erosive marine environments and thus provide the most complete record of volcanic activity. Wide aerial distribution across sedimentary facies boundaries, near-instantaneous emplacement, correlative chemical signatures, and the presence of minerals suitable for radiometric dating make ash layers an excellent stratigraphic marker in marine sediments and provide constraints on the temporal evolution of both, the volcanic source region and the ash-containing sediment facies. On-shore stratigraphic successions of tephra layers are generally based on the distinct composition of tephras. In west-central Nicaragua for example (section 2.1), late Pleistocene to Holocene tephras were emplaced by highly explosive eruptions, with a combined erupted mass of 184 Gt (DRE), that are distributed into 9 dacitic to rhyolitic eruptions (84%) and 4 basaltic to basaltic-andesitic eruptions (16%). Widespread eruptive masses from explosive volcanism are usually underestimated, even when the most distal parts of the on-shore distribution fans, normally not preserved in terrestrial environments, are included. If on-shore tephras can be correlated to offshore deposits like those in Central America (sections 2.2 and 2.3), the revised erupted magma mass show that the tephras account for 65% of the total arc magma output. This enables the minimum estimation of long-term average magma production rate at each volcano and over whole arcs. Using their unique compositional signatures, tephras facilitate the determination of provenance as well as the reconstruction of emplacement processes of volcanoclastic marine sediments, in accordance with regional geotectonic settings (section 2.4). Ash layers in marine sediments offshore Central America can provide time constraints for submarine landslides at the continental slope, as they probably act as weak layers where sliding initiates (section 2.5). Variations in the sedimentation rates on the slope, constrained by bracketing tephras of known age, can be attributed to periods of intense erosion on land likely triggered by tectonic processes. In the case of the incoming plate these changes can be due to changes in bend-faulting activity across the outer rise, which elicit erosion and re-sedimentation. Additionally, ash layers in Central America can help determine the duration of active and inactive periods in the multi-stage growth history of fluid venting sites (section 2.6). Cyclicity in the marine tephra record along the Pacific Ring of Fire yields a statistically significant detection of a spectral peak at the obliquity period, which is related to crustal stress changes associated with ice age mass redistribution and therefore supports the presence of a causal link between variations in ice age climate, continental stress field, and volcanism (section 2.7). To summarize, the seven manuscripts presented here highlight the benefit of tephrostratigraphy as a major tool in geology, and show that the tephra record on-shore and, especially in the marine environment, have a spectrum of possible applications to decipher the causes and temporal variability of geological processes