An isotope is one of two or more species of atoms of a chemical element with the same atomic number (same number or protons in the nucleus) and position in the periodic table and nearly identical chemical behavior but with different atomic masses and physical properties. Every chemical element has one or more isotopes.
A landslide is the movement of rock, debris or earth down a slope. They result from the failure of the materials which make up the hill slope and are driven by the force of gravity. Landslides are known also as landslips, slumps or slope failure.
Slump, in geology, downward intermittent movement of rock debris, usually the consequence of removal of buttressing earth at the foot of a slope of unconsolidated material. It commonly involves a shear plane on which a back-tilting of the top of the slumped mass occurs. The plane is slightly concave upward and outward and separates the slump block from unslumped material of the same character. In sedimentary strata the slumping material generally bends elastically until the rock strength is exceeded, when it breaks and moves rapidly. See also sedimentary structure.