Inés Galindo

Depth of origin of magma in eruptions.

Many volcanic hazard factors - such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses - relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11–15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011–2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide.

Dike-induced reverse faulting in a graben

Normal-fault slip of the boundary faults of a graben is commonly attributed to dike-induced stresses. Here, however, we report for the first time clear field evidence of a large dike-induced reverse-fault slip on a fault associated with a volcano-tectonic graben. The measured reverse faulting of at least 5 m occurs in the Holocene rift zone of northern Iceland. The reverse slip has apparently occurred on an existing normal fault as a result of over pressure of a nearby 6–13-m-thick 8 ka feeder dike. A numerical model of the dike-fault interaction supports our interpretation. The results indicate that dikes, particularly potential feeder dikes, may cause large reverse slips on nearby normal faults. This conclusion should improve the general understanding of geodetic deformation during volcanic unrest periods and may help forecast dike-fed eruptions.