Joel Ruch

Dike-fault interaction during the 2004 Dallol intrusion at the northern edge of the Erta Ale Ridge (Afar, Ethiopia)

Received 17 July 2012; revised 29 August 2012; accepted 4 September 2012; published 12 October 2012. [1] During continental rifting the interaction between faulting and magmatic intrusions is not well understood. Using InSAR and seismicity, we show that a 0.06 km 3 dike was intruded along the Dallol segment, Ethiopia and was accompanied by a Mw 5.5 earthquake and associated fault slip along the western flank of the rift. The intrusion was fed by a previously unidentified magma chamber under Dallol. The total seismic moment release was 2.3 10 17 Nm, 10% of the geodetic moment. This is a higher proportion than during the 2005–2009 Dabbahu rifting episode, which ranged between 1–4% of the geodetic moment. A larger component of faulting occurs at Dallol than at Dabbahu segment, a feature we interpret to be related to the proximity (10 km) of the Dallol segment to the rift margin, where welldeveloped faults facilitate slip. Citation: Nobile, A., C. Pagli, D. Keir, T. J. Wright, A. Ayele, J. Ruch, and V. Acocella (2012), Dike-fault interaction during the 2004 Dallol intrusion at the northern edge of the Erta Ale Ridge (Afar, Ethiopia), Geophys. Res. Lett., 39, L19305, doi:10.1029/2012GL053152.

Detachment depth revealed by rollover deformation: An integrated approach at Mount Etna

This work was partially funded by INGV and the DPC‐INGV project “Flank”, and partially by the ASI (SRV project).

Flank instability structure of Mt. Etna inferred by a magnetotelluric survey

This paper presents a magnetotelluric (MT) survey of the unstable eastern flank of Mt. Etna. We take thirty soundings along two profiles oriented in the N-S and NW-SE directions, and from these data recover two 2D resistivity models of the subsurface. Both models reveal three major layers in a resistive-conductive-resistive sequence, the deepest extending to 14 km bsl. The shallow layer corresponds to the volcanic cover, and the intermediate conductive layer corresponds to underlying sediments segmented by faults. These two electrical units are cut by E-W-striking faults. The third layer (basement) is interpreted as mainly pertinent to the Apennine-Maghrebian Chain associated with SW-NE-striking regional faults. The detailed shapes of the resistivity profiles clearly show that the NE Rift is shallow-rooted ( 0–1 km bsl), thus presumably fed by lateral dikes from the central volcano conduit. The NW-SE profile suggests by a series of listric faults reaching up to 3 km bsl, then becoming almost horizontal. Toward the SE, the resistive basement dramatically dips (from 3 km to 10 km bsl), in correspondence with the Timpe Fault System. Several high-conductivity zones close to the main faults suggest the presence of hydrothermal activity and fluid circulation that could enhance flank instability. Our results provide new findings about the geometry of the unstable Etna flank and its relation to faults and subsurface structures.

Stress transfer in the Lazufre volcanic area, central Andes

eruptive centers situated in an area larger than 1800 km 2 and (2) a small-scale uplift located at Lastarria volcano, which is the only volcano to show strong fumarolic activity in decades, with most of the clear deformation apparently not observed before 2000. Both the large and small uplift signals can be explained by magmatic or hydrothermal sources located at about 13 km and 1 km deep, respectively. To test a possible relationship, we use numerical modeling and estimate that the depth inflating source increased the tensile stress close to the shallow source. We discuss how the deep inflating source may have disturbed the shallow one and triggered the observed deformation at Lastarria. Citation: Ruch, J., A. Manconi, G. Zeni, G. Solaro, A. Pepe, M. Shirzaei, T. R. Walter, and R. Lanari (2009), Stress transfer in the Lazufre volcanic area, central Andes, Geophys. Res. Lett., 36, L22303, doi:10.1029/2009GL041276.

From structure- to erosion-controlled subsiding calderas: evidence thresholds and mechanics

Collapse calderas evolve by increasing their depth/diameter ratio. To properly characterize caldera evolution, a structural S/D (ratio between structural subsidence and ring–fault diameter; Ss/Ds), and a topographic S/D (ratio between topographic caldera depth and topographic caldera width; St/Dt), are considered. We review the evolution of the A.D. 2000 Miyakejima caldera, with two concentric ring faults at earlier collapsing stages, and erosion of its wall, accumulating debris on the floor, at later collapsing stages. While St/Dt and Ss/Ds show a similar increase at initial stages, when Ss/Ds ∼0.33 the Ss/Ds becomes significantly different from St/Dt: while continuous caldera subsidence monotonically increases Ss/Ds, the erosion of the wall and the filling of the floor decrease St/Dt. This evolution finds close similarities with recent caldera collapses of Krakatau (1883), Katmai (1912), Fernandina (1968), Tolbachik (1975–1976), Pinatubo (1991), and Dolomieu (2007). Analog experiments mimic the observed variation, evolving from a depression controlled by the activity of the double-ring faults to that controlled by the erosion of the wall and sedimentation at the floor. These natural and modeling results show that the control on the shape of mature calderas (Ss/Ds > 0.07) and approaching Ss/Ds = 0.3–0.4 passes from a mainly structural to a mainly erosional control. Both St/Dt and Ss/Ds are needed to describe the evolution of a collapse and the processes accompanying it. Evaluating St/Dt and Ss/Ds allows proper description of the precise evolutionary stage of a caldera and of the relative importance of the structural and erosional processes and allows making semiquantitative comparisons between evolutionary stages.

Volcanic product detection after the 2010 Merapi eruption by using VHR SAR data

The volume estimation of products is critical for volcanic hazard mitigation, especially for lahars (mudflow) occurrences during rainy season at Merapi, and at active volcanoes subject to lahars elsewhere. Lahars can affect inhabited areas around a volcano, even several years after an eruption. In this work, we present an innovative approach to detect and estimate the volume of pyroclastic flow deposits. We exploited data collected from the very high resolution SAR sensor on board of the COSMO-SkyMed satellite constellation. By comparing a pre-eruption airborne Digital Surface Model (DSM) with a new one obtained applying SAR Interferometry technique to COSMO-SkyMed data, we estimate the volume of the pyroclastic material emitted during the 2010 Merapi eruption. Results show pyroclastic flow deposit thicknesses of up to 75 m that fill canyons on flank of volcano, and are observed up to 16 km far from the mountain summit. The total volume of the deposits is around 117×106 m3.

Seismicity Associated With the Formation of a New Island in the Southern Red Sea

Volcanic eruptions at mid-ocean ridges are rarely witnessed due to their inaccessibility, and are therefore poorly understood. Shallow waters in the Red Sea allow the study of ocean ridge related volcanism observed close to sea level. On the 18th December 2011, Yemeni fishermen witnessed a volcanic eruption in the Southern Red Sea that led to the formation of Sholan Island. Previous research efforts to constrain the dynamics of the intrusion and subsequent eruption relied primarily on interferometric synthetic aperture radar (InSAR) methods, data for which were relatively sparse. Our study integrates InSAR analysis with seismic data from Eritrea, Yemen, and Saudi Arabia to provide additional insights into the transport of magma in the crust that fed the eruption. Twenty-three earthquakes of magnitude 2.1–3.9 were located using the Oct-tree sampling algorithm. The earthquakes propagated southeastward from near Sholan Island, mainly between December 12th and December 13th. The seismicity is interpreted as being induced by emplacement of a ∼12 km-long dike. Earthquake focal mechanisms are primarily normal faulting and suggest the seismicity was caused through a combination of dike propagation and inflation. We combine these observations with new deformation modeling to constrain the location and orientation of the dike. The best-fit dike orientation that satisfies both geodetic and seismic data is NNW-SSE, parallel to the overall strike of the Red Sea. Further, the timing of the seismicity suggests the volcanic activity began as a submarine eruption on the 13th December, which became a subaerial eruption on the 18th December when the island emerged from the beneath the sea. The new intrusion and eruption along the ridge suggests seafloor spreading is active in this region.