Tahiti is known as a tropical paradise for good reason, but the island is actually made of two volcanoes connected by a narrow and short isthmus. The larger one, Tahiti-Nui, is older, with lava rocks dated to 1.7 million years ago. Tahiti-Iti, the smaller one, has lava less than a million years old.

Both shield volcanoes have collapsed, and heavy erosion from rainfall has radically changed their appearance from all that time ago when they formed.  This Landsat 7 image makes all that very clear... though I imagine from ground level it's far, far tougher to see.

Original image

Credit: NASA Earth Observatory image by Jesse Allen and Robert Simmon, using Landsat data from the U.S. Geological Survey.