Surface water seeps through the soil and becomes groundwater. The water then seeps to depths of over and flows underground to a distant aquifer. Groundwater seeps through the geotextile and flows through the stone to an outfell. Natural seeps of methane and carbon dioxide occur. The water then seeps down to the magma and is heated to the boiling point. It is found in ditches, quarries, seeps, flushes, marshes and pools. Hot springs, streams, fumaroles, natural gas seeps and volcanic domes dot the caldera floor landscape. This acid flows out of the seeps and portals of the mine. The lake water seeps through the soil into the Karez Gallery. The canyons have much exposure of clay, over which water often seeps. Brine pools are another seabed feature, usually connected to cold seeps. Water seeps into the rock, and at night it expands as it gets colder. Cold seeps, locally known as "bubbling reefs" (), are found in the northern Kattegat. This is a naturally-occurring marshland where water seeps above-ground all year round. The first wells were drilled into Pitch Lake oil seeps in 1866.