Interstitial Water

(pore water), subterranean water in the pores of rocks, soils, and bottom sediments of oceans, seas, and lakes. Two types of interstitial water are distinguished, according to the size of the enclosing interstices: macrocapillary and microcapillary. In interconnected macrocapillary pores, which have a radius of more than 10^–5 cm, interstitial water moves easily by force of gravity; this is called free, or gravitational, water. Interstitial water in microcapillary pores, whose radius is less than 10^–5 cm, is influenced by the surface forces of mineral particles; it has the properties of bound water, which is separated by pressing out, centrifuging, or drawing out under a vacuum.

In the late 1960’s the term “interstitial water” came to be used primarily for water enclosed in microcapillaries; in marine geology this water is also called silt water. The water is present in all rocks and bottom sediments, but it is especially characteristic of clay rocks and sediments. Geological reserves of this water are significantly greater than reserves of free water. The interstitial water of the microcapillary pores is the medium in which the processes determining the mass exchange between hydrous and solid phases of rocks and sediments occur most intensively. For this reason, interstitial water is important in the history of subsurface water, the diagenesis of sediments, and the catagenesis of rocks. It affects the strength and behavior of rocks when engineering structures are erected.

In the USSR, V. I. Vernadskii attached great importance to the geochemical study of microcapillary water. In the 1940’s, methods were developed to identify interstitial water and analyze it chemically from marine sediments (S. V. Bruevich) and rocks (P. A. Kriukov). Since 1968, the interstitial water in the bottom sediments of the oceans and seas has been investigated systematically by American scientists working on the deep-sea drilling project based on the research ship Glomar Challenger.