July 28, 2012 - 70 Million Years of Pacific Plate Movement: The map above shows significant volcanoes over the last 3,500 years, in and around the Pacific Ocean. Almost all noteworthy volcanoes and earthquakes occur along Convergent plate boundaries (see below).
There are four types of plate boundaries: (1) Divergent boundaries, where new crust is generated as the plates pull away from each other – red lines, (2) Convergent boundaries (see picture belwo), where crust is destroyed as one plate dives under another – green lines, (3) Transform boundaries, where plates slide horizontally past each other – yellow lines and (4) Plate boundary zones, broad belts in which boundaries are not well-defined and the effects of plate interaction are unclear – none shown.
Almost all momentous volcanoes, and earthquakes, occurred in and around the Pacific Ocean near Convergent boundaries (Ring of Fire – see below). This was the case with the mega earthquakes, and subsequent tsunami’s, in Japan (2011) and Indonesia (2004). Significant volcanoes also occur on Convergent boundaries. This was the situation with Krakatau (1883) and Tambora (1815) in Indonesia. The country of Iceland is an example of volcanoes occurring in a Divergent boundary zone (not shown).
Volcanoes can also occur over “Hot-Spots” such as Hawaii (USA), Yellowstone (USA), the Galapagos Islands (Ecuador) and the Azores (Portugal).
Over the past 70 million years, the combined processes of magma formation, volcanic eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian “hot-spot” has left a long trail of volcanoes across the Pacific Ocean floor (see purple line marked by the “Pacific Plate Shift” box). The Hawaiian Ridge-Emperor seamounts’ chain extends some 6,000 km (3,730 miles) from the “Big Island” of Hawaii to the Aleutian Trench off Alaska. The Hawaiian Islands themselves are a very small part of the chain and are the youngest islands in the immense submarine mountain chain composed of more than 80 volcanoes. A sharp bend in the chain indicates that the motion of the Pacific Plate abruptly changed about 43 million years ago, as it took a more westerly turn from its earlier northerly direction. Why the Pacific Plate changed direction is not known.
As the Pacific Plate continues to move west-northwest, the Island of Hawaii will be carried beyond the hotspot by plate motion, setting the stage for the formation of a new volcanic island in its place. This process is already under way. Loihi Seamount, an active submarine volcano, is forming about 35 km (22 miles) off the southern coast of Hawaii. Loihi already has raised about 3 km (1.9 miles or 10,000 feet) above the ocean floor to within 1 km (0.6 miles or 3,170 feet) of the ocean surface. As Loihi continues to grow; it will become the next island in the Hawaiian chain. In the future, Loihi will eventually become fused with the Island of Hawaii, which itself is composed of five volcanoes knitted together: (1) Kohala, (2) Mauna Kea, (3) Hualalai, (4) Mauna Loa, and (5) Kilauea.
Notice that the “recent” submarine mountain chain, marked by the short purple line closest to Hawaii, points directly toward Japan and the Kamchatka Peninsula of Russia! (Credits: USGS and NOAA).
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