Controls on the geometry of a Holocene crater row: a field study from southwest Iceland

Abstract

The Reykjanes Peninsula rift zone in southwest Iceland is a highly oblique segment of the Mid-Atlantic ridge system which accommodates NW-SE extension during rifting episodes that consist of eruptions and normal faulting, and E-W left-lateral shear strain along strike-slip faults during longer amagmatic periods. Dominant tectonic features on the peninsula are a series of generally NEstriking, sub-parallel eruptive fissures and normal faults, and a cross-cutting zone of N-S striking, right-lateral strike-slip faults. The last series of rifting episodes ended in 1227, and a proposed 1,000 year cyclicity predicts the start of a new series of eruptions within the next 200 years. In order to more accurately characterize the nature of eruptions on the Reykjanes Peninsula, we present a new, spatially accurate map of the ∼2,350 year old Sundhnúkur crater row in the western part of the peninsula, which was examined in detail in order to determine the structural controls on crater row geometry and to understand the interactions that take place between eruptive fissures and pre-existing geological structures. Volcanism is sometimes influenced by small perturbations in the surroundings such as gravitational loading, topography, changes in crustal properties or the presence of fault zones, but there are few field examples showing how fissures are influenced by these pre-existing structures. We identify 27 fissure segments, ranging in strike from 006°to 053°, with varying spacing and overlap between them. Significant local variability in strike and stepping sense of segments occurs in proximity to topographic highs as well as within zones of faulting that pre-date the crater row. Strike also varies at the northern end of the crater row as it approaches a region of older crust at the rift margin. Our data support numerical and laboratory modeling results which show that local topography, pre-existing fractures and crustal properties influence the path taken by magma on its way through the shallow crust.

Revised earthquake hazard of the Hat Creek fault, northern California: A case example of a normal fault dissecting variable-age basaltic lavas

“…The westward migration of successive scarp system segments of the Hat Creek fault suggests that Cinder Butte and its underlying magmatic system may have focused the development of the active portion of the fault in the proximity of Cinder Butte. Such a model is consistent with documented examples of magmatic systems affecting fault growth and orientation in response to local stress perturbations related to magma pressure (Clifton and Schlische, 2003;Clifton and Kattenhorn, 2006;Rowland et al, 2007;Gudmundsson et al, 2009) or the topographic and mechanical attributes of volcanic constructs (Friese, 2008;Jenness and Clifton, 2009). Lava fl ows from Cinder Butte covered the northern end of the Pali scarp; however, the Active Scarp subsequently dissected these lavas and curved toward the center of Cinder Butte (Fig.…”

Varying styles of magmatic strain accommodation across the East African Rift

“…We infer that extension‐normal cones represent aligned swarms of dikes, with orientations controlled by the regional extensional stress field. As these basins comprise abundant fault and dike systems oriented normal to the regional σ 3 , many of the dikes could potentially be focused along preexisting structures [ Le Corvec et al ., ], as is interpreted for interacting fissures and faults in magmatic rifts in the Reykjanes Peninsula, Iceland [ Jenness and Clifton , ], and the Main Ethiopian Rift [ Casey et al ., ; Mazzarini et al ., ].…”

The 2019 Eruption Dynamics and Morphology at Ebeko Volcano Monitored by Unoccupied Aircraft Systems (UAS) and Field Stations

“…As deposition of eruptive material often obscures direct views of the underlying structures, general morphological expressions can be indirectly assessed where aligned vents and craters indicate underlying zones of structural weakness [8]. Craters may form in groups and alignments [9], developing into crater rows linked to dikes [10] or multiple vents along active and elongated fracture zones [11]. Volcano craters that are controlled by tectonic stress fields and preexisting crustal fault structures are also affected in terms of their geometry, stability and breaching direction [12], highlighting the importance of investigating these possible interactions.…”