Where Mountains Form? A mountain is a large mass of rock that rises a great distance above its base. Are formed due to tectonic activity – due to convergence of plate boundaries Most of the world’s mountains are formed in long belts due to the whole side of plates crashing into other plates A mountain belt is a region where mountains are forming or have formed in the past Mountain Belts, Continental Margins A cordillera is a mountain belt that runs down the length of a plate A mountain belt is made up of smaller groups of mountains called mountain ranges example: Cascade range is part of the North American Cordillera Some mountains lie on current plate boundaries – such as the Himalayas, while others lie on boundaries that existed millions of years ago – such as the Appalachians. Continental Margins A Continental Margin is a boundary between continental crust and oceanic crust Active continental margins occur along plate boundaries, while passive continental margins occur at the boundary that marks a continent and the oceanic crust. Mountain building takes place along active continental margins only. Passive continental margins are areas where sediment accumulation takes place How do Mountains form? At convergent plate boundaries – the stress due to pushing of plates causes fracturing, folding and stretching Types of stress: Compression: rock layers squeezed inward, tends to make rock layers thicker and shorter Tension: rock layers being stretched, tends to make rocks thinner and longer Shear stress: rock layers being pushed in two different, opposite directions. Tends to distort the shape of the rocks This is an upward fold of strata; found in the Alps. Folds During plate collisions, stress can cause rock layers along continental margins to crumple into folds. Folds are described as being anticline and syncline Anticline: is an upfold in the rock layers, a syncline is a downfold in the rock layer. The two sides of a fold are called limbs – limbs represent the intensity of the folding. Limbs may be gently dipping, steeply dipping, straight up or down or even overturned. The compass direction of the fold or of the rock layers exposed at the surface along the fold is called the strike Faults Faults: a fault is a break in the lithosphere along which movement has occurred The part of the fault above the fault plane is called the hanging wall and the part below is called the footwall. A normal fault occurs when a hanging wall moves down with respect to the footwall. What would you call a single-limbed fold like this? A normal fault occurs in areas where tension is pulling the crust apart A reverse fault occurs when the hanging wall moves up with respect to the footwall. Reverse faults are caused by compression A thrust fault is a reverse fault in which the fault plane dips 45 degrees or less from the horizontal Thrust faults are common in many mountain belts. A strike slip fault, the rocks on opposite sides of the fault plane move horizontally past each other example – San Andreas fault Extremely long strike slip faults are found in the Himalayas. Joints: like faults, are breaks in bedrock. Joints are breaks along which no apparent movement has occurred. Joints provide channels through which fluids enter and move through bedrock. Related posts: Plate Tectonics & Continental Drift Proof What are Plate Tectonics? A Plate Tectonics Flip Book Answers How and Where Volcanoes Form What are Earthquakes?