There is friction between the plates, so that crinkling of the upper plate occurs. This crinkling represents pressure and release, which can result in violent jerking and upheavals, sometimes snapping to create new cliffs or jutting rock. Those riding on the upper plate during these moment will be heaved skyward and dashed, with scarcely a safe place to cling to.
Subduction can release pressure by pushing flakes of land that separate from lower stratas forward .
Push a wooden block against some flaky pastry, and watch the top flakes simply fly forward, separating from the pastry. This thrust can be sudden and projectile, with the rock flake then crashing down again. Pressure and release can also create crumpling land where such activity is not expected. Mountains and valleys have likewise been formed because of crumpling, horizontal pressure, and this will happen again during the forthcoming shift. It breaks, and moves into the point of least resistance which is upward into the air.