Dallol (hydrothermal system)

Dallol lies in the northern Danakil Depression of Ethiopia's Afar region, within an active rift setting. The Smithsonian Institution's Global Volcanism Program lists it as a volcanic feature at about 14.242°N, 40.3°E, with an elevation of −48 m. The wider depression includes a salt plain formed from marine evaporite deposits.

Dallol's dome-like landform is unusual: research describes it as being made principally of uplifted salt layers rather than exposed volcanic rocks. Scientists relate its development to interactions among buried evaporites, magmatic intrusions, groundwater and geothermal fluids. The complex includes a summit depression, hot springs, fumaroles, salt deposits and pools of acidic brine. Field studies have documented brines with very low pH, high salt concentrations and temperatures that can approach or exceed 100°C in some settings; conditions vary among sites and over time.

Dallol's hydrothermal features are dynamic. Geological mapping and analysis of aerial and satellite imagery indicate changes in the distribution of geothermal activity; researchers linked a reactivation episode to a 2004 dyke intrusion. Smithsonian records also summarize reports of phreatic, or steam-driven, activity, including an explosive event in 1926 and a reported event in early 2011. Such reports should not be confused with evidence of a conventional lava-producing eruption at the dome.

Dallol offers researchers an opportunity to study how rifting, magmatism, salt deposits and hydrothermal fluids interact. Its combination of acidity, heat and salinity has also made it relevant to research on environmental limits for life and to comparisons with potentially harsh environments elsewhere. Scientific interpretations of the site's geology and habitability rely on field measurements and continue to develop.