High-resolution magnetic investigation of hydrothermal circulation in the Danakil Depression

The Danakil Depression is an active divergent boundary opening between the southern Red Sea rift and the Afar triple junction at a rate of ~1 cm/yr. Despite its geological interest, it is becoming increasingly difficult to study due to regional political instability and extreme environment. Our study area, located between the Erta ‘Ale volcano and Dallol, exhibits thick salt layers and iron-rich clay intercalations locally covered by mud volcanism deposits. The heat from the volcanic rift segment and the occasional influx of saltwater from Lake Karum create a unique hydrothermal system on land. In 2019 we collected ground magnetic field data around the main active hydrothermal fissure to investigate the magnetic signature of this hydrothermal system.  Our data show a clear linear magnetic anomaly low associated with the fissure, indicating a loss of magnetization due to the active hydrothermal activity. Local anomaly lows are observed at hydrothermal pools and in areas of subsurface bubbling. Apart from the hydrothermal areas, a relatively uniform magnetic anomaly is observed above the resurfaced reddish mud. Its slow decay away from the fissure may correspond to the progressive attenuation of the superficial iron-rich mud layer considered the most likely coherent magnetized source in the area. Our inference of the iron-rich mud layer as the bearer of a coherent magnetization that is altered by the hydrothermal activity needs however to be confirmed by sample analyses.