In the geosciences, pore water is the water content that is contained in fine cavities in the soil and in the rock near the surface. Depending on the substrate, the water content can range from a few percent (e.g. in the case of granites ) to around half (in the case of clayey rocks) and is of decisive importance for the mechanical and hydrological behavior of the soil and must be taken into account when measuring the bulk density .
Changing water content can lead to a. on the phenomena of denudation , floor creep , the formation of mudslides and other movements on slippery slopes . The frost burst in pores and crevices can trigger landslides , but also contribute to the loosening of arable soil (see frost blast ). In general, the pore water is responsible for the conditions in the groundwater, its slow currents and its chemistry , and the proportion of pores in the soil filled with air or water is responsible for the nutritional conditions of the plants.
In the slow solidification of sediments , the compaction , the decreasing proportion of the pore water due to pressure and heat inside the earth plays a decisive role. The water diffuses, following the pressure gradient, into higher rock layers, the pores shrink and the density of the rock increases by a few percent to 20 percent, depending on the original consistency and current depth. Rocks that contained large amounts of pore water when they were deposited are often used as storage rock for oil or natural gas formed in the depths . Remnants of the water mostly come to light as salt water during extraction.
The pore water pressure is a measure of the undirected pressure of the pore water in loose or solid rock. Beyond the hydrostatic pressure , a pore water overpressure arises in substrates with low water permeability if the water content corresponding to the equilibrium state only occurs with a delay as a result of a load acting on the soil.