EXERCISE 2.8: Determining Ancient Plate Direction: Footprints of a Moving Plate

The Hawaiian Islands, located in the Pacific Ocean far from the nearest mid-ocean ridge, are an excellent example of hot-spot volcanic islands (see the figure below). Volcanoes on Kauai, Oahu, and Maui haven’t erupted for millions of years, but the island of Hawaii hosts five huge volcanoes, one of which (Kilauea) has been active continuously for more than 30 years. In addition, a new volcano, already named Loihi, is growing on the Pacific Ocean floor just southeast of Kilauea. As the Pacific Plate continues to move, Kilauea will become extinct and Loihi will become the primary active volcano.

Image p. 43 Ages of Hawaiian volcanoes in millions of years (Ma). Map of Hawaii islands Part 1.c

Geologists use the azimuth method to describe direction precisely. In the azimuth method, north is 0°, east is 090°, south is 180°, and west is 270°, as shown in the following figure. The green arrow points to 052° (northeast). To practice using the azimuth method, estimate and then measure the directions shown by arrows A through D, using a protractor on your screen.

Image p. 44 The azimuth method. An azimuth is the direction measured in degrees clockwise from north on an azimuth circle. An azimuth circle consists of 360 degrees. Ninety degrees corresponds to east, 180 degrees is south, 270 degrees is west, and 360 degrees and 0 degrees mark north.

What is the azimuth of arrow A?

Arrow A's azimuth is approximately 52° (northeast) when using the azimuth method. This method measures directions in degrees clockwise from north, making 0° north, 90° east, 180° south, and 270° west.

In the azimuth method for precise direction, Arrow A's azimuth is approximately 52° (northeast) from the reference point of north being 0°, east 90°, south 180°, and west 270°. This technique aids geologists in describing orientations accurately. The Hawaiian Islands exemplify hot-spot volcanic activity, with Kilauea currently active. Over millions of years, the Pacific Plate's movement will render Kauai, Oahu, and Maui extinct, while Loihi, a new volcano southeast of Kilauea, will become the primary active volcano. The azimuth method helps geologists analyze and predict the dynamic geological processes shaping Earth's surface, enhancing our understanding of plate tectonics.