Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. Of course, earthquakes do occur at rifts, though not at the severity and frequency of some other boundaries. Some have argued that not all hot spots are sourced from deep within the planet, and are sourced from shallower parts of the mantle. By using the age of the eruptions from hot spots and the direction of the chain of events, one can identify a specific rate and direction of movement of a plate over the time the hot spot was active. Some have speculated an earlier start to the hotspot, tying it to the Columbia River flood basalts and even 70 million-year-old volcanism in Canada’s Yukon. How subduction initiates are still a matter of some debate. Instead of earthquakes found along a narrow boundary, collision earthquakes can be found hundreds of miles from the suture between the landmasses. One famous example is the Mississippi Valley Embayment, which forms a depression through which the upper end of the Mississippi River flows. With subduction ceasing with the collision, there is not a process to create the magma for volcanism. They are the only places on Earth where the new oceanic lithosphere is being created via slow oozing volcanism. Normal and reverse faulting and divergent and convergent boundaries tend to obscure, bury, or destroy these features; transform faults generally do not. While some scientists often assume that mantle plumes do not move, much like the plumes themselves, this idea is under dispute. When two plates come together, The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. Collision zones are known for tall mountains and frequent, massive earthquakes, with little to no volcanism. In trenches, the ocean can be more than twice as deep, with the Mariana Trench approaching a staggering 11 km. In places where transform faults are not straight, they can create secondary faulting. There are three types of boundaries according to the way the tectonic plates interact with each other. The continental lithosphere is always lower in density and is buoyant when compared to the asthenosphere. A location where continental lithosphere transitions into the oceanic lithosphere without movement is known as a passive margin (e.g., the eastern coasts of North and South Ameri-ca). © Adobe Systems Incorporated. Tectonic Plate Boundaries Hananeel morinville. A chain of volcanoes often forms parallel to the boundary, to the mountain range, and to the trench.