ABSTRACT
Thirteen, mostly basaltic, lava fields cover a large area (180,000 km2) of western Saudi Arabia. Three main characteristics of the lava fields in Saudi Arabia may have helped making them suitable places for groundwater accumulation: long periods of eruptions with long gaps of no eruption allowing for continental deposits to accumulate; the basalts are densely fractured and vesicled; and in many cases the lava fields were deposited in basin-like structures leading to minimal discharge from the aquifers. The northern part of Harrat Rahat covers an area of about 2000km2 and has a thickness of up to 300m. The aquifer has a saturated thickness of up to 70m and is made up of three units: weathered topmost part of the basement, pre-basalt sands and gravels, and the fractured basalts. The aquifer contains moderate amounts of good-quality water and receives little recharge. Basaltic aquifers can be important sources of water locally but have to be properly managed.
