What is sea floor spreading? Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.
What are some of the major land forms that are created from plate movement? As plate movement occurs, a long chain of mountains form gradually on the ocean floor as magma piles up along the crack, which is called the oceanic ridge.
How were the Mariana Islands formed? As plate tectonics presumes; the Asian continent and the North and South American continents are moving and that the crust of the continents are composed of different material. The edge of these plates are believed to be moving in such a manner that one moves under the other and the cataclysmic forces that result push material upward to form the islands.
What evidence exists today that the plates are still moving and that the islands are ancient volcanoes? Plate tectonics has been developed to explain the observed evidence for large scale motions of the Earth's crust. This explains that the fitting together of the coasts of the continents on the opposite side of the Atlantic Ocean express geologic formations and fossils found on the opposite sides. A geologically active mid-ocean ridge running along the central Atlantic between the opposite coasts, where as the bottom sediments get thicker and the farther one travels from the ridge, and the rocks on the sea floor on one side of the ridge show magnetic bands that are mirror images of rocks found on the opposite side of the ridge.
What is an atoll? An atoll is an island of coral that encircles a lagoon partially or completely. There are different types of reefs that make up the components of an atoll. A fringing coral reef surrounds a volcanic island in the tropical sea and will grow upwards as the island subsides, becoming an "almost atoll" (barrier reef island). The fringing reef becomes a barrier reef for the reason that the outer part of the reef maintains itself near sea level through biotic growth, while the inner part of the reef falls behind, becoming a lagoon because conditions are less favorable for the corals and calcareous algae responsible for most reef growth. Subsidence then carries the old volcano below the ocean surface, but the barrier reef remains. At this point, the island has become an atoll.
Why are atolls mainly found on the Pacific? Atolls are only found in warm tropical waters, which are the main cause of growth of the tropical marine organisms. The volcanic islands are located beyond the warm water temperature, which contain reef building organisms that become seamounts as they subside and are eroded away at the surface. The islands are located where the ocean water temperatures are sufficiently warm for upward reef growth to keep pace with the rate of subsidence.
