4. The Ring
of Fire
Expedition Menu
1.
Introduction
2. Global Distribution
3. Earthquakes & Plate Boundaries
4. The Ring of Fire
5. Convergent Boundaries
6. Atlantic Ocean
7. Atlantic Ocean II
8. Alaska Earthquake
9. Vertical Slice
10. 3-D Look
11. California Plate Boundaries
Earthquake Depth in Earth and Magnitude scale at right
You can see, once again, that the earthquake distribution follows the plate boundaries (and vice versa).
See chart of symbols at right showing depth of earthquake in different collors and the magnitude according to size of dot.
On the map in your expedition worksheet, draw a rough sketch of the distribution of the epicenters around the Pacific and label the continents on your sketch. Include the location of seamount chain which extends northwest from the Hawaiian Islands, and bends to the north; this string of volcanoes (active on the Big Island and inactive elsewhere) is the Hawaiian-Emperor seamount chain. Draw in location of Tokyo and San Francisco on map.
The locations of deep earthquakes in the western and northern Pacific, down to as deep as 670 kilometers within the Earth, lie along the western edge of the Pacific Plate -- from Russia southward to New Zealand.
The depth of these earthquakes, combined with the rapid northwest movement of the Pacific plate (remember problems at end of the expedition on plate motions) provide evidence that the plate is being pulled to the northwest by slabs of lithosphere that sink down subduction zones in the western Pacific. Oceanic lithosphere, because of its high density when it gets old and cold, sinks back into the mantle at subduction zones along convergent plate boundaries.
Thus the Pacific plate is created at mid-ocean ridges along its eastern margin at the East Pacific Rise and Juan de Fuca Ridge, travels to the northwest and ultimately is recycled into the Earth by subduction along its western and northern boundaries.
Answer the questions in your worksheet.
Contact Don Reed
Dept. of Geology
San José State University
©Copyright 1999
Last Updated on June 21, 1999
How does
the "Ring of Fire" relate to the distribution of volcanoes?