Day 5:  September 9, 2005

Reporting:

Elizabeth Creek (Events 1, 2), Corinne Hume (Events 3, 4), and Robin Matoza (Events 5, 6) (Group 4).

All coords UTM, WGS84

First we stopped by a small hole in the frozen lava. By looking at the surrounding landscape and several other holes, we determined that the lava flow had wrapped around a tree, quenching against the bark. Upon closer examination of the Ohia trees in the area, we decided that maybe the lava had come up over a meter and what we were seeing was the lava wrapped around the branches instead of the trunk. Because the bombs that were ejected (bombs because they were still molten when they landed) built up on one side of the tree, it was possible to determine the direction of flow, and thus the direction that the source was located. We were cautioned to consider differences in topography when examining differences in highs and lows of lava, and also told that directed eruption columns can make piles of tephra nearby.

From this vantage point, we obtained a very good view of the lava lake crust and “bathtub” ring formed from the lake in the present crater. We also noticed that magma emerged from a fissure at our highly elevated position at the crater rim. It seems like it would have been more energy efficient for the lava to have come up at the crater instead of fissuring at the crater rim, but we have to keep in mind that we have a top down view, and the magma has a bottom up view. It didn’t know about the crater, and took the easiest route to the surface it could find. More on the tree moulds: the lava agglutinated from puopui, or from the original eruption.

In this area, a short-lived eruption occurred, covering an ohia forest with lava and leaving tree molds behind. We could tell these were tree molds because there were bark impressions, charcoal, and occasionally trees in the interior of the molds. The lava formed a crust around the trees because the water in the trees turned into steam removing heat and allowing the molten rock to solidify. Because of this interaction, we expected the interior of the tree molds to have a glassy surface with few vesicles, with vesicle size and number increasing towards the outside. This was not observed in the field. Instead, the inside of the tree mold had a thin layer (~2cm thick) with many large vesicles, then a thicker layer similar to what we expected, that was denser towards the inside with few or no vesicles and larger vesicles near the outside (8 cm). The vesicles in the thin layer on the inside were probably preexisting in the lava flow, because the first part to hit the trees was from a partially cooled surface that acted as a plastic. The height of the tree molds showed the highest level of lava flow. As the lava found a better drainage path, the thickness of the lava flow decreased leaving the tree molds behind. The direction of flow can be determined using tree molds by observing the seam that forms when lava wraps around the tree. The seam is opposite to the direction of flow. Also, erosion on the lower portion of the tree mold may be observed where the flow hit. If there is agglutinated material on top of tree molds, the thicker to thinner direction can be the flow direction. Agglutinated material suggests that area is close to the eruptive site, as it is ejected from the vent and cannot travel very far. We observed shelly pahoehoe lava, another indicator of close proximity to the source. We observed what we thought to be vents in the area. One area, we thought to be the main eruptive site, because it was the highest, and had collapsed in the middle. This area was also covered with agglutinates, was a bright red color (evidence of high heat), and had many cracks and fissures.

A’a flows have a rough, rumbly surface, with levees on the sides. The middle of aa flows, where the flow has the greatest velocity often contain accretionary lava balls where the rubble on the surface dips into liquid center of the flow and sticks pieces of the rough surface together. In cross section, aa flows have a rough surface, a solid dense lava interior, and a rubble bottom. The interior of an aa flow exhibits cooling cracks that are columnar and have large vesicles in the center, the area that cooled last. We observed Pele’s hair and reticulite that were probably from Pu’u O’o.

From this vantage point we could see the active portion of the Pu’u o’o lava flows into the ocean. We discussed the hyaloclastic (“broken-glassy”) form the lava would acquire from this initial magma-water interaction. This first layer of hyaloclastics dipping away from the shoreline would be subsequently overlain by lava flows. The main gas plume was dominantly white – indicative of steam, while a secondary haze of gas was probably ‘laze’ or lava haze (HCl) created from magma volatizing sea water. We could also smell the SO2 volcanic smog – ‘vog’.

At this locality we were dropped off in front of an impressive lava flow cut by the road -exposing its cross section. At the bottom of the section were rubbly deposits, overlain by the inflated ‘core’ of the flow – complete with banded vesiculation revealing the succession of ages of various portions of flow. The lava flow was capped by the pahoehoe surface which had gorgeous ropey texture flowing over such man made obstacles as coaxial cable, the old road, and a road sign. In the centre of the flow was at least one lava tube – large enough to crawl into – with a frothy base (slow cooling) and a drippy top.

We also noted several morphological features of the flow. Firstly, the absence of levees and more laterally dispersed pahoehoe flow compared to the A’a flow of event 4. Secondly, we noticed that increase in slope correlated with a higher fraction of A’a vs. pahoehoe lava. Thirdly, an age progression of lava flows was present – with the older flow appearing as a dark brown colour (vs. black for the most recent flow) which was still present as isolated “Kipuka” in some parts of the current flow. The entire area could be considered a massive delta fan made from lava flows down the fault scarps bounding this edge of volcanism before the ocean, and eventually Loihi. Finally, the flows were dusted with a light coating of reticulite and pele’s hair from Pu’u O’o.