Day 6:  September 11, 2004

Reporting:

Lucian Parry, Jaime Ricci, Kristin Lawrence (group 5)

Creek bed exposing 1881 flow; Kaumana Caves; Mauna Kea Cinder Cone (Kipuka Pu'u Huluhulu); Mapping exercise of Mauna Loa flows

Support Files: Aerial photograph for class exercise; Daily track, a plot of the route, and track data, including GPS tracking data as a txt file and as an xls file.Start at KMC

The first stop on our field excursion today was a creek bed located in the beginnings of the saddle in between Mauna Kea and Mauna Loa. A historic lava flow originating from the northeast rift zone of Mauna Loa in 1881 is exposed within the creek bed. Given the climate of the region there is significant weathering of the flow, having extensive soil development and plant growth. The lava contains abundant nutrients for the flora. Below the 1881 flow lays the Pahala ash, which is significantly leeched, from all the rainwater. The volcanic glasses have been converted to clay by hydration, leaving aluminum and iron and titanium oxides. Mining of Bauxite in this region is economical due to the leeching of the lava and ash deposits.

The next stop was the Kaumana Caves. This cave system is the remnant lava tube that fed the 1881 flow. The flow lasted for ~280 days and consisted of multiple pulses. These pulses are visible in the caves as pahoehoe terraces. At this stop one of our valiant leaders attempted to blaze a new trail and failed miserably, we had to send a search and rescue team after him. Luckily, he was safe and sound and rewarded us with FREE ice cream.

Mauna Kea Cinder Cone (Kipuka Pu'u Huluhulu)

For lunch we stopped at a cinder cone formed by Strombolian style of eruption during the early Holocene. This feature could have been created in as little as a few months due to high extrusion rates and steady state dynamics. It is considered a "wart" on the side of Mauna Kea with younger flows from Mauna Loa surrounding it.  A classic Strombolian feature is the bread crust bombs found surrounding the cinder cone. These bombs often form a spindle like feature while flying through the air and before they cool, they expand and produce a cracked crust similar to bread (hence the name). The tephra of this cone is unconsolidated and deposited at the angle of repose, which is ~ 30¡. These cinders are considered of classic Hawaiite composition.

Our last stop of the day consisted of providing ground-truth observations for an aerial photograph of a region near the top of Mauna Loa. In this region, we were just above the trade winds and the contrast in weathering with the first stop is readily apparent. In fact, the lack of weathering is useful because the color differences between the lava flows of different ages are clear. There are 4 different units located in the region with definite stratigraphic relations seen throughout.

An unusual feature found in this region is an accretionary lava ball. They are thought to form continuously during an aa flow, similar to a snowball. An alternative theory, not found in textbooks, is that they form from skylights in lave tubes, and then seen down slope from their origin. The skylight is an opening in the lave tube after roof collapse. This chunk of tube then becomes the nucleus of the accretionary lava ball.