Pop-Tarts have a sugary filling sealed inside two layers of thin, rectangular pastry crust. The resulting bagel is puffy with a moist crust. Volcanoes result primarily from the melting of subducted crust material. Subduction initiates as oceanic lithosphere slides beneath continental crust. The crust and filling are pre-cooked. The densest objects are likely composed of rock with a thin crust of ice. In Ganymede a thick and solid ice crust then formed. Pegmatite may be produced by low degrees of partial melting of the crust. It formed as a result of the upwelling of magma from within the Earth's crust. Reverse faults indicate compressive shortening of the crust. It is distinguishable by its length and crisp crust. Temperature increases with increasing depth into the Earth's crust. Granitic rocks predominate throughout the crystalline remnants of the surviving Archean crust. Plates include both oceanic crust and continental crust. Tidal forces affect both the Earth's crust and oceans.