Day 10:  September 14, 2005

Reporting:

Steve Macalello, Patrick Senge, Paul Peshette

Though labeled as caves, spelunking into the fern and algae covered mouth of the two opposing openings quickly reveals this as a single collapsed lava tube. The northwest-southeast trending tube was a large path for the 1881 Mauna Loa flow that reached the outskirts of the town of Hilo. The tube is accessible in both directions, with a flashlight needed in either case. If traveling down the tube, after climbing over debris fallen from the ceiling, the tube shows a division of at least two distinct separate surges of lava subsequently draining from the tube. The first, the forming flow, which left the tube empty and the second, approximately filling the tube half-way and cooling along the edges of the tube leaving behind a shelf of very smooth pahoehoe. The tube narrows greatly in some places, requiring almost getting down on hands and knees, implying damning of the lava at cold spots in the tube, while chambers with heights of perhaps five meters or more are present in some places. It is unknown to this group how far one could travel downstream, though the sign at the entrance states that there is no marker within the tube notifying the division between public and private land. If traveling upstream in the tube one must duck beneath a shelf to enter into the passable route. This course markedly curves uphill and has much fallen debris for about a kilometer, where the tube splits, with the left choice leading into as yet unexplored darkness, and the right leading to a series of skylights which lead into jungle and a massive roof collapse with trees growing within the tube itself. As far as could be told the tube does seem to continue, though because of time constraints, was not explored by any member of this group.

Meaning “Little Hill of Much Shaking” this wonderful little picnic hill provided great scenic views of both Mauna Loa (Long Mountain) to the south and Mauna Kea (White Mountain) to the north, along side Saddle Road. The NOAA observatory was visible on the western side of Mauna Loa at an elevation of approx. 11,000 ft. This observatory is known for the essential research done in investigation of atmospheric CO2 levels for many years, especially by Charles Dave Keeling from Scripps Institution of Oceanography. Jack Lockwood devised a plan after the early 1980s Mauna Loa eruptions to save the observatory from a possible doom by building a “lava diversion” in the form of an upside down Y with the observatory in the cup of the Y, surrounded by ten meter tall walls. This diversion was built in 1985 out of the A’a flows covering much of the mountain at the elevation, and though is said to be “working perfectly”, has yet to actually come face-to-face with any lava.

Pu’u Huluhulu itself is a kipuka cinder cone, covered in greenery and surrounded by Mauna Loa lava flows. To the west of the cone is a late 19th century wall, an anthropologic feature integrated into a younger flow, actually acting as an impedance to the 20th century pahoehoe lava and collecting along its edge. Compositionally, Pu’u Huluhulu is a Hawaiite/alkali basalt, Strombolian type cinder cone with lead isotope ratios of Mauna Kea reference. The cones at this elevation are usually not tuff cones because of the lack of water to generate a hydrovolcanic eruption, except at the top where glaciers can begin to act as a body of standing water. When looking at Mauna Kea, the volcano shows much more surface topography than Mauna Loa, this is mainly due to the prevalence of cinder cones spread out all over the face of the mountain, but also because of the glaciation occurring at higher elevations. The last known eruption of Mauna Kea occurred five to six thousand years ago and was composed of more alkali basalt. This correlates with the life-cycle of a plume-based volcano, which according to the model begins with alkali basalts, transfers to a theoleiitic melt and then finishes with alkali again. Mauna Loa and Kilauea are in, or nearly still in, the theoleiitic, shield-building stage. The alkali stage pulls into the melt more incompatibles like sodium and potassium, but also volatiles, like water and carbon dioxide, thus making the lava more eruptive than effusive and leading to the build up of cinder cones. Some of the cinder cones almost line up radially to Mauna Kea, and are thought to possibly be radial fractures from which the lava was able to escape more easily from depth similar to those seen on Mauna Loa with spatter cones along them.

To prove to one’s self that Pu’u Huluhulu is in fact a cinder cone, inspection of an old quarry on the southwestern side provides close looks at the interior of the cone. Such inspection gives light to the general composition of the hill being generally lapilli-sized scoria similar to the marker layer seen in the Keanakakoi Ash Member. This quarry area also provides an interesting challenge with the presence of two high angle, close to vertical lava dikes, which could have been from Mauna Loa flows pressurized enough to infiltrate the cinder cone, or somehow part of the cinder cone either from the summit or somehow from within the cone itself.

Blocks or Bombs? The difference is blocks are broken rocks and bombs cooled while traveling through the air. This means that the bombs show signs of aerodynamic cooling and are covered by less (if not non-) vesiculated, quenched surfaces.

On the way up the road to the NOAA observatory there are a series of radio antenna that are surrounded by a variety of lava flows, aerial photographs provide an excellent opportunity to study these. There are four major units of lava in this region. Two of these are Pahoehoe, one prehistoric and the other from 1881, while the other two are A’a, the older showing Pahoehoe transitioning into A’a, and the younger looking slightly more oxidized than the 1881 flow, but providing a channel for it in many places.