In geography, an oasis is an isolated area in a desert, typically surrounding a spring or similar water source, such as a pond or small lake. Oases also provide habitat for animals and even humans if the area is big enough. Rain showers provide subterranean water to sustain natural oases, such as the Tuat. Substrata of impermeable rock and stone can trap water and retain it in pockets, or on long faulting subsurface ridges or volcanic dikes water can collect and percolate to the surface. Wilderness arid sahara. 4K UHD 3840×2160.