Hawaiian Volcanoes Field Course 2005
UCSD ERTH 170/198 -- UCD GEL 138/198

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Day 2:  September 6, 2005

Reporting:

Mike Buga, Amanda Bush, Sarah Flores

Keanakakoi Ash Member
Local Time Date Lat / Lon Elevation
11:54:00L  9/6/05 2147244 N 262236 E 1093 m 

Pahoehoe and aa lava cascades down southern wall of Kilauea Caldera. We examined the stratigraphy of the wall to determine the chain of events that created the features we observed:

  1. Basalt base formed, creating what would become caldera wall; block-like appearance
  2. Lava drained and caldera formed
  3. Lava flow over rim into caldera
    - pahoehoe first entered with high temp, low viscosity
    - pahoehoe could not stretch at rate of flow as slope increased, so it broke apart and became aa
    - alternating vertical strips of pahoehoe and aa formed as a result
  4. Lava lake forms in caldera, truncating prior flow down caldera wall
  5. Lava lake ledge formed due to draining of lava in center of lake and overlying crust subsiding
    - Slicken sides form where the lake crust scraped the cooler, partially solidified sides of the lake
Local Time Date Lat / Lon Elevation
12:34:00L 9/6/05 2146815 N 261704 E 1101 m

We stopped further west where the 1971 flow flowed into the caldera and again observed the order of events. Pyroclastic debris was deposited first. Next, the fault block formed to create a channel (there is also evidence that the channel may have formed from lava erosion). During the 71 eruption a high speed lava flow wound around the corners of the channel and rode up high on the outside wall of the turns. The final event was another flow from within the caldera that spread over the mouth of the 71 lava river.

Local Time Date Lat / Lon in Deg/Min.DecMin Elevation
14:00:00L 9/6/05 2146366 N 261455 E 1135 m

Measured strat columns of Keanakakoi Ash Member, which was deposited between 1500 and 1790 CE. Each group recorded thickness, bedding characteristics, sorting, composition, and color (using the Munsell chart) of the sub-units. At the base of the column was a basalt layer, followed by a vitric base. The Keanakakoi Ash consists of several layers of ash and lapilli with a lithic-rich layer near the top of the column. The uppermost layer is a breccia, consisting of occasional block and block sags.

Local Time Date Lat / Lon in Deg/Min.DecMin Elevation
15:52:00L  9/6/05 2146449 N 262389 E 1137 m

We stopped at the top of the southern end of the Keanakakoi Crater. At various points around the crater we could see where lava flowed down into the caldera during the 1974 eruption, suggesting that the crater formed first from the draining of the chamber and the subsequent collapse of the caldera. It is likely that, in addition to the 74 flow, a sill or vent supplied the caldera with lava to create a new lake in the bottom of the caldera. We also noted that this is not the source of the Keanakakoi Ash Member.

Local Time Date Lat / Lon in Deg/Min.DecMin Elevation
16:22:00L  9/6/05 2147194 N 263404 E 1149 m

At the intersection of Chain of Craters Road and Crater Rim Drive we could again see the section of the Keanakakoi Ash Member. At this point, the entire section was only approximately 1 meter thick. This suggests that this location was more distal from the source when compared to the location used for our strat columns. The Tradewinds are also responsible for the distribution of the ash, blowing the particles in a southwest direction. Also at this location, the tephra and ash compose non-consolidated layers of the vitric base. The pumacious lapilli stone layer was highly distinctive, and was topped by a lithic-rich unit. There were no signs of the upper-most breccia.