This earthcache is located along the Makapu'u lighthouse trail. The trail is paved almost the whole way, but, like many trails on the island, it is fairly steep. Please bring water, snacks, sunscreen, and anything else you may need while hiking. Parking is available at the trailhead, but please be mindful of the no parking signs and areas. ATTEMPT THIS EARTHCACHE AT YOUR OWN RISK.
The geological history of Hawaii is closely tied to the movement of tectonic plates in the Earth's crust. Hawaii is located in the middle of the Pacific Plate, which is one of the largest tectonic plates on Earth. As the Pacific Plate moves over a hot spot in the Earth's mantle, magma rises to the surface and forms volcanoes. Hawaii's position in the middle of the Pacific Plate and its proximity to a hot spot in the Earth's mantle has made it a hotbed of volcanic activity, creating a unique and dynamic landscape that continues to shape the island chain today. The volcanic activity on Oahu eventually ceased, and the island was subjected to a period of erosion and weathering. Rivers and streams carved deep valleys into the volcanic rock, creating the dramatic landscapes that we see today.
A fissure eruption, also known as a volcanic fissure, fissure vent, or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts which run first in lava channels and later in lava tubes. After some time, the eruption tends to become focused at one or more spatter cones. Small fissure vents may not be easily discernible from the air, but the crater rows or the canyons built up by some of them are. The dikes that feed fissures reach the surface from depths of a few kilometers and connect them to deeper magma reservoirs, often under volcanic centers. Fissures are usually found in or along rifts and rift zones. Eruptions of this type can cause tuff cones to form and alter the landscape.
Tuff cones are created by explosive eruptions from a vent where the magma is interacting with either groundwater or a shallow body of water as found within a lake or sea. The interaction between the magma, expanding steam, and volcanic gases resulted in the production and ejection of fine-grained pyroclastic debris called ash with the consistency of flour. The volcanic ash comprising a tuff cone accumulated either as fallout from eruption columns, from low-density volcanic surges and pyroclastic flows, or a combination of these. Tuff cones are typically associated with volcanic eruptions within shallow bodies of water.
Two distinct tuff cones formed by volcanic activity are in view at this site. Using the cache page and your observations from the site please answer the following questions to be credited with a find:
1) Where do fissure eruptions eventually become focused?
2) Where are fissures usually found along or in?
3) Are tuff cones generally formed with or without water interaction?
4) Of the two tuff cones in your view, one is significantly taller. What factors do you think influenced the size difference between the two?
5) Based on your view do you think the pyroclastic debris that formed these tuff cones was made up of similar material or differing material?
6) Do you think the tuff cones are the same size and shape now as when they were formed?
7) OPTIONAL Post a picture of your group having a great time!