These happens in areas where two plates move apart (diverge). The rising conventional currents of magma in the upper mantle moves laterally, drags and causes the plates to split and move apart. Along plate boundaries, magma (balsaltic) wells up from the mantle, cools and forms MID-OCEANIC RIDGES on the ocean floor. An example would be the MID-ATLANTIC RIDGE in the middle of the Atlantic Ocean, which forms when the American plates on the west and the Eurasian and African plates on the east move apart. These areas are also zones of volcanic activity and sea-floor spreading because of such upwelling of magma. As the upwelling of magma in these area causes new crust to be formed, therefore it is also known as the zone of construction. These Ridges are characterized by recent and frequent volcanic activity (submarine). Magma is injected into faults or rifts. For example, Iceland, Surtsey and the Azores is a section of the mid-Atlantic Ridge. The crest of a mid-oceanic ridge is marked by parallel faults and a rift valley as a result of tension.