<P> A shield volcano has a gently sloping cone due to the low viscosity of the emitted material, primarily basalt . Mauna Loa is the classic example, with a slope of 4 ° - 6 ° . (The relation between slope and viscosity falls under the topic of angle of repose .) The composite volcano or stratovolcano has a more steeply rising cone (33 ° - 40 °), due to the higher viscosity of the emitted material, and eruptions are more violent and less frequent than for shield volcanoes . Besides the examples already mentioned are Mount Shasta, Mount Hood and Mount Rainier . </P> <P> When plates collide or undergo subduction (that is--ride one over another), the plates tend to buckle and fold, forming mountains . Most of the major continental mountain ranges are associated with thrusting and folding or orogenesis . Examples are the Jura and the Zagros mountains . </P> <P> When a fault block is raised or tilted, block mountains can result . Higher blocks are called horsts and troughs are called grabens . A spreading apart of the surface causes tensional forces . When the tensional forces are strong enough to cause a plate to split apart, it does so such that a center block drops down relative to its flanking blocks . </P> <P> An example is the Sierra Nevada Range, where delamination created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States . </P>

Which type of plate boundary is most associated with earth's major mountain chains