Stop 4: Lanai Overlook
Just a few minutes drive around the coast from Hanauma Bay is a turn-off on the road that is called Lanai Overlook. This stop gets its name because on a clear day one can not only see the island of Molokai, but also Lanai (and sometimes Maui too!). At this stop, tourists can enjoy not only the view across the channel to Molokai, but also crashing surf, really unusual landforms made from volcanic ash and, because of its location on the island, it is very often very sunny.
The first thing you see as you get out of your car and look at the landscape is the unusual rock that makes up the cliffs at the Lanai Lookout. Here we see a detailed view of the ash, which was created when a volcanic eruption took place just offshore perhaps 300,000 years ago. Rather than produce a lava flow, the hot magma interacted with the sea water to produce violent steam explosions that fragmented the magma to produce the ash. We can tell that these were violent offshore eruptions because along with the ash, we often find white pieces of coral (as seen here). This coral was once at sea level but was torn from the reef during the explosions.
People who like a bit of adventure can get much closer to the ocean at this point on the island, and can also see many of the different rock layers in detail. Here we see an interesting series of rocks, with a lava flow lying on top of all the ash layers. This lava flow tells geologists that right at the end of the eruption the volcanic crater was no longer flooded by seawater, so that no more explosions took place, allowing the formation of a lava flow.
If you turn around and look behind you, you can see the source of some of the ash at this site; Koko Crater. Because it is made of ash, Koko Crater has been heavily eroded by the rain, so that the sides have deep valleys carved into them.
Much of the coastline from Hanauma Bay to Koko Crater is made from tuff, which formed during explosive eruptions as hot lava flows came in contact with sea water and generated violent steam explosions. Here we can see that these eruptions took place close to the shore, since a portion of the coral reef was broken off during a blast and thrown into the air, only to land in wet ash, creating a small indentation in the surface layers. This piece of coral is about 10 cm in diameter.
From here you can continue on to Stop 5 on the ground.
Return to Southeast Oahu Virtual Field Trip
Author: Peter Mouginis-Mark
Copyright by P. Mouginis-Mark
Curator: Lori Glaze