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- Ormö, Jens, et al.
(author)
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Comparison of clast frequency and size in the resurge deposits at the Chesapeake Bay impact structure (Eyreville and Langley cores): Clues to the resurge process
- 2009
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In: Geological Society of America Special Papers, 458. - 9780813724584 ; , s. 617-632
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Book chapter (other academic/artistic)abstract
- Collapse and inward slumping of unconsolidated sedimentary strata expanded the Chesapeake Bay impact structure far beyond its central basement crater. During crater collapse, sediment-loaded water surged back to fill the crater. Here, we analyze clast frequency and granulometry of these resurge deposits in one core hole from the outermost part of the collapsed zone (i.e., Langley) as well as a core hole from the moat of the basement crater (i.e., Eyreville A). Comparisons of clast provenance and flow dynamics show that at both locations, there is a clear change in clast frequency and size between a lower unit, which we interpret to be dominated by slumped material, and an upper, water-transported unit, i.e., resurge deposit. The contribution of material to the resurge deposit was primarily controlled by stripping and erosion. This includes entrainment of fallback ejecta and sediments eroded from the surrounding seafloor, found to be dominant at Langley, and slumped material that covered the annular trough and basement crater, found to be dominant at Eyreville. Eyreville shows a higher content of crystalline clasts than Langley. There is equivocal evidence for an anti-resurge from a collapsing central water plume or, alternatively, a second resurge pulse, as well as a transition into oscillating resurge. The resurge material shows more of a debris-flow–like transport compared to resurge deposits at some other marine target craters, where the ratio of sediment to water has been relatively low. This result is likely a consequence of the combination of easily disaggregated host sediments and a relatively shallow target water depth.
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| 2. |
- Pinel, Virginie, et al.
(author)
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Consequences of local surface load variations for volcanoes monitoring: Application to Katla subglacial volcano, Iceland
- 2009
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In: The VOLUME Project. VOLcanoes: Understanding subsurface mass moveMEnt. Edited by C.J. Bean, A.K. Braiden, I. Lokmer, F. Martini, G.S. O´Brien. - Dublin, Ireland. - 9781905254392 ; , s. 25-39
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Book chapter (other academic/artistic)abstract
- Surface load variations occur frequently in the vicinity of volcanoes inducing deformation and stress field perturbations that can be recorded by geophysical monitoring. It is thus necessary to discriminate these perturbations from those caused by shallow magma movement and to understand their potential influence on themagmatic plumbing system. Discrimination can be performed by modelling the deformation induced by surface load variations using integration of Green's function. This method was applied to the Katla volcano located beneath the Mýrdalsjökull ice cap, Iceland, where an annual cycle in ice load occurs as well as a gradual ice retreat. We also estimated pressure changes induced by the seasonal ice load variation within a magma reservoir, and calculated the deformation field and the Coulomb stress changes induced by the combined effect of the ice load variation and the magma pressure re-equilibration. Seismicity rate response to the seasonal perturbation strongly depends on the shape and state of the magma reservoir. Finally, introducing a rupture criterion, we conclude that, in the case of spherical or horizontally elongated reservoir and a slow magma inflow, eruptions at Katla volcano are more likely during the summer period, which is consistent with historical observations.
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