Formation of the Hawaiin Islands

The Hawaiin islands are made up of 107 volcanoes stretched across 1500 miles of the Pacific Ocean. They were formed over about 70 million years by the movement of the Pacific plate to the Northwest over a stationary hotspot where magma wells up from the earths mantle.

This means that the further away from the hotspot an island is the older it should be, and this is borne out by observation. First we can use radiometric dating to get absolute dates for each island, which look like this:

(source)


Consequently, if we then run the clock backwards using near-present day rates of 3.4 inches a year these dates coincide with those islands being over the stationary hotspot.

Second, and this is one you can do yourself, we can look at the amount of erosion and weathering that have taken place. Obviously the older an island is the more eroded it should be with the oldest islands actually having been flattened by waves and eventually sink below the surface. This is exactly what we find.

(source)

The later point is something that’s pretty easily observed even without any complex understanding of radioactive decay or weathering.  For example, here’s Hawaii, one of the youngest islands in the chain, notice the nice tall mountains:

Now let’s jump to one of the last (oldest) islands in the chain, Kure:

Notice a difference in the amount of erosion that's taken place?

Even the ancient Hawaiins believed that the islands got younger as they approached Hawaii,

“The possibility that the Hawaiian Islands become younger to the southeast was suspected by the ancient Hawaiians, long before any scientific studies were done. During their voyages, sea-faring Hawaiians noticed the differences in erosion, soil formation, and vegetation and recognized that the islands to the northwest (Niihau and Kauai) were older than those to the southeast (Maui and Hawaii). This idea was handed down from generation to generation in the legends of Pele, the fiery Goddess of Volcanoes. Pele originally lived on Kauai. When her older sister Namakaokahai, the Goddess of the Sea, attacked her, Pele fled to the Island of Oahu. When she was forced by Namakaokahai to flee again, Pele moved southeast to Maui and finally to Hawaii, where she now lives in the Halemaumau Crater at the summit of Kilauea Volcano. The mythical flight of Pele from Kauai to Hawaii, which alludes to the eternal struggle between the growth of volcanic islands from eruptions and their later erosion by ocean waves, is consistent with geologic evidence obtained centuries later that clearly shows the islands becoming younger from northwest to southeast.”
(source)

Subsequent Note:

A noticeable shift in the Hawaiin-Emperor Seamount chain was caused by the Pacific plate changing direction from 50 to 42 million years ago. As with the Hawaiin chain the trend of consistently older radiometric dates continues as does the relative amount of erosion.
(source)

Further reading material:
http://www.soest.hawaii.edu/GG/HCV/haw_formation.html
http://www.enotes.com/earth-science/…land-formation
http://hvo.wr.usgs.gov/volcanoes/