Day 2:  September 7, 2004

Reporting:

Marcel Croon, Jennifer Duncan, Ian Nagy (group 3)

Volcano House; Old Kilauea Iki crater rim road; Overlooking Kilauea Iki from the trail; Thursten (Nahuku) lava tube; Stratigraphy of Kiluea Iki crater lava lake compared to wall rock; Kiluea Iki crater vents; Interrelations between Kilauea Iki crater lava lake basalt crust and shelly pahoehoe basalts from eruption vent; Pu’u Pua’i cinder / spatter cone; Pahoehoe to ’A’A flow transition zone in Kilauea Iki crater lava lake

Support Files:   A plot and the location of the overall hiking track is given in Figure 2-1 and Table 2-1, respectively.

The first stop on our hike was at the Volcano House, a charming hotel overlooking the Kilauea crater. This hotel was an interesting anthropogenic site. In addition to its spectacular view off the back porch (photo IMG_0684: Overview of Kilauea crater), the lobby of the Volcano House was decorated with artists’ renditions of Kilauea over time, including paintings preceding the 1924 eruption, when the crater was an active lava lake. The Volcano House has been in operation since 1846, when a sugar planter opened his grass hut for housing at a dollar a night. The current building was built in 1941 and includes 42 rooms, all furnished with rare Koa wood furniture.

The road that we hiked after leaving the Volcano House was once the Kiluea Iki crater Rim Road; however, sections of the road were destroyed during a large landslide associated with a nearby earthquake. 1975 and 1983 were bad years for the month of November on Hawaii, as they were disrupted by magnitude 7.3 and 6.6 earthquakes, respectively. During the 1983 earthquake, a large landslide carried sections of the road off into the caldera. The faulting caused by the earthquake is blatantly obvious as one strolls down the road, as breaks in the yellow line or sharp uplifting of the pavement accent the disruptions to the underlying landscape. 

Hawaiian earthquakes are particularly dangerous because they often cause tsunamis.  The reaction times for tsunamis caused by earthquakes on the rift zones are so short that there is little time to safely clear an area before disaster strikes.

Overlooking Kilauea Iki from the trail

We stopped to look down on the Kilauea Iki crater. In 1959, this crater filled with 120m of molten lava.  As it started to cool, USGS seized the opportunity to monitor the lava lake for the rates and types of crystallization during cooling. They studied this by lowering a drill rig down onto the floor of the lava lake and drilling into the lake (150m deep) to monitor (photo IMG_0716: Drill holes in lava lake of Kilauea Iki crater). This study was an important addition to the study of magma crystallization. 

Kilauea Iki violently erupted on November 14, 1959.  It is one of the many pit craters that characterize the rift zones on Kilauea.  These craters were not formed by explosive events, but by the collapse of a floor over underlying lava.  This crater was a part of a large venting region on a shield volcano named Ailaau, which was active until the late 15^th century.  The Kilauea Iki crater formed in the 16^th century and has since been the site of several lava lakes, with the most recent in 1959. 

The 1959 eruption was a fissure eruption with a spectacular fire fountain.  The fissure eventually went to a point eruption with the mound at the edge of Kilauea Iki as its source.  This mound is a cone layered with spatter and cinders.  The lava filled the lake to a depth of 120m.  As the surface of the lava lake eventually lowered, one side of the mound collapsed, perhaps because it had previously been supported by the edge of the lava lake and could no longer support itself as lake level dropped.

We encountered a lush rainforest as we descended stairs towards Thurston lava tube (photo P9070041: Thurston (Nahuku) lava tube). Lava tubes efficiently transport magma over large distances with little loss of heat. Lava tubes often form within pahoehoe lava flows, when the top part of the flow is exposed to air and solidifies. The underlying lava is insulated, losing little heat as it continues to flow within the tube. When the last of the lava drains out, a hollow tube remains. Walking through this tube, we noticed how the ceiling seemed to have a dripping texture, much like the “bathtub rings” of the Kiluea Iki crater that we would observe later.

As we descended the walls of Kiluea Iki crater, we described this host rock of the lava lake outcropping along the trail. The rock is 1 to 2% vesicular, having cooled slowly enough (as intrusive or slowly cooling in a flow) to degas and form a fine grained structure. While the chemical composition of the basalts on the floor of the Kiluea Iki crater lava lake is the same as the host rock, their physical structure is different. The crater floor basalts at the surface were quenched rapidly by air and had no time to degas forming the glassy texture and making it 40% vesicular at least. The olivine phenocrysts found in both host rock basalts and lava lake basalts were formed as magma cooled slowly and differentiated in the magma chamber. A new batch of magma carried these olivine crystals to the surface of the volcano. Also an occasional pyroxene crystal was found in the host rock.

The surface of the lava lake itself provided a glimpse into plate tectonics. Hot material below a solid crust convects and rises through the surface at thin areas. More dense crust near the walls of the crater sinks, much like the oceanic lithosphere slab pull which is the engine for plate tectonics.

Next we stopped at a few steam vents in the middle of the Kilauea Iki crater. Although the lava lake, of basalt composition, is no longer molten, having crystallized between 1000°C and 800°C, the rock is still hot, slowly cooling over time by conduction since the latest eruption in 1959. Convection is a much more efficient cooling mechanism but naturally only possible with fluids. Water seeping into cracks in the rock is heated and released as steam. We measured the temperature of steam being released at two vents between 40°C and 80°C.
 
White precipitates are deposited on the rocks near vents (photo DSC01305: Kilauea Iki crater white precipitates). Steam, still have ions dissolved, rises out of the vent and condenses on the rock. As the water evaporates dissolved silica and sulfate will precipitate. As this process continues, bumps of precipitate form.
 
Green microbes were indicated in one of the vents. They live off of chemical energy obtained from their surroundings.
 
Volcanologists observe the expansion and contraction of this area by drilling pillars into the rock at the surface of the lava lake. Installed GPS receivers precisely measure the position and these data are compared to previous data. This way changes in size, shape, and activity of the crater lake are monitored.

The dome visible at this event formed during the 1959 eruption in the Kilauea Iki crater lava lake. Interesting feature at this location is the interrelation of freshly formed crust at the surface of the lava lake and the wall rock formed by spatter (glutenite). Looking at the stratigraphy and properties of the interacting basalt lavas and rocks reveals the interaction and formation history. 3 processes of basalt rock formation are identified at this event:

1. Spatter basalt: The spatter (shelly pahoehoe basalt) indicates the close proximity of the eruption vent.
2. Lava lake crust: Glassy and highly vesicular at surface becoming gradually less vesicular downwards. The high vesicularity is caused by fast cooling; the lava has no time to degas and bubbles are captured in the solidifying rock. When the lava is drained below the freshly formed thin crust it drips at the bottom forming “stalactites” (photo IMG_0719: Kilauea Iki crater lava lake crust).
3. Lava lake crust basalt plastered on the spatter basalt wall rock: Lava is cooling and plastered on the colder spatter basalt wall rock (bath tub edge)

The thin crust formed at the lava lake surface is draped over the dome in broken pieces indicating the flow was still moving when the lava lake drained causing the fresh crust to collapse. At some places it scratched the freshly formed soft plastered crust by sliding over it. The spatter basalt is exposed on the edge and on top of the dome. Relations were new spatter rock is deposited on top of the lava lake crust are also visible. This shows the dynamic process of interrelation during this phase of the eruption, which could have taken place in a period as short as a couple of days.

The Pu’u Pua’I cinder / spatter cone (photo P9070006: Pu’u Pua’I cinder / spatter cone) is formed in 1959 by a lava fountain forming the cinder and is interlayered with spatter basalt formed during the same eruption event . A cinder cone is typically formed in a time period of weeks or mostly a couple of months. Typically a cinder is formed in a late stage of the eruption event and is non-explosive. The channel at the bottom of the cone is probably formed during a late phase of the cone formation and contributed to filling the Kilauea Iki crater lava lake. The “dune” shape of the cone is caused by tephra blown by the wind in the SW dominant direction. The red color visible on the surface is oxidization (rust) of iron in the rock due to H₂O gas (hot water steam) escaping from the rock. The hot water temperature generates the oxidization energy.

At this event a pahoehoe lava flow is transited into an ’A’A lava flow. Pahoehoe lava is lumpy and occasionally ropy of form and has a smooth glassy skin. The lava  flows under its skin, and is less viscous than ’A’A flows due primarily to high temperature (> 1100°C) and high dissolved gas content. Loss of temperature and gas and increase in basal friction (or shear strain) as the lava is flowing causes the flow to transform into an ’A’A lava flow. The colder and more viscous ’A’A lava flow overruns itself and has a “brecciated” skin. At this location pieces of freshly solidified pahoehoe are incorporated in the ’A’A lava flow (photo P9070052: Kilauea Iki crater Pahoehoe to ’A’A flow transition zone).