Day 3:  September 7, 2005

Reporting:

Roi Granot, Julie Hernandez, Ashley Heers

At the Steaming Bluffs, we saw several steam vents aligned on an E-W trending fault (parallel to the caldera bounding faults). The steam temperature was roughly 80°C (based on previous measurements), and its pH was between 5 and 5.5 (based on actual measurements). There were no deposits around the vents, and no obvious odors; vegetation and microorganisms grew on and near the vents. From these observations we concluded that the steam consisted mainly of water vapor and carbon dioxide. dO18 and dD isotopes suggest that the source for the water vapor was meteoric. The permeability of the faults in this area allows water to percolate and interact with rocks heated by magma at depth.

From the Steaming Bluffs, we walked a few minutes to the Sulfur Banks. Here we saw several fumaroles with yellow sulfur deposits, with no sign of life. Like the steam vents, the fumaroles are aligned on an E-W trending fault. The temperature of the fumarole gases here is greater than 100°C, but can reach extreme temperatures, depending on the internal pressure. We measured the pH of the gases as ~1.5, though previous measurements were more acidic (near 0). The gases were probably H2S or SO2; H2S smells like rotten eggs and SO2 like strong bleach. These acidic gases have altered some of the surrounding rocks to kaolinite clays, which can lead to instability. Fumaroles are distinguished from steam vents by the source of their gases: the volatiles in a fumarole result from magmatic degassing, whereas the gases in a steam vent result from the interaction between water and hot rock.

We headed SE from the Visitor Center to Kilauea Iki, site of the first well-studied eruption of the 1900’s. Kiluaea Iki is a pit crater that was formed in the mid 15th century when the Aila’au Shield collapsed. In November 1959, the eruption broke out of the southern wall of the Kilauea Iki crater. A lava lake filled the crater to a depth of 120 m. This lava lake hosted the most detailed study of magmatic crystallization (by USGS).

From the overlook of the Kilauea Iki Lava Lake, we walked to the Thurston Lava Tube. Lava tubes are formed in molten pahoehoe lava flows. The surface of the lava flow cools convectively and conductively to form a crust of solidified material. Beneath this crust, lava is insulated and continues to flow. As the supply of lava diminishes, a tube is formed.

After exploring the Thurston Lava Tube, we headed down the Kilauea Iki crater to the lava lake. The rocks exposed at the “shore” of the Kilauea Iki Lava Lake are glassy and pumiceous, containing abundant subhedral olivine phenocrysts (grain size 2 – 10 mm) with chromite inclusions. The eruptions that produced these rocks were some of the few that resulted in lava containing such phenocrysts. The presence of these rare phenocrysts suggests that the magma remained in the magma chamber long enough to partially crystallize before being erupted. Possibly, the magma was isolated from the main magma chamber.

From the “shoreline”, we proceeded towards the center of the Kilauea Iki Lava Lake, and examined two drill holes. The holes were emitting steam of pH 5.5; there were no deposits nearby. We concluded that the steam resulted from groundwater interactions, like the steam vents in Event 1. The USGS used these drill holes to examine how magma bodies cool and crystallize. We discussed the idea that the magma body cooled more rapidly from the top towards the center (by conduction of heat to moving air and hydrothermal convection) than from the bottom/sides towards the center (by conduction to surrounding rocks).

From the drill holes, we walked west and observed a ridge forming the western edge of the lava lake. The ridge was formed by earlier eruptive activity, probably from the crater wall. It exposes different still stands of the lava lake. The center of the ridge was eroded by the 1959 flow that formed the lava lake.

We continued west. On the SW wall of the crater we saw the spatter cone (part of Pu’u Pua’i) made by the 1959 eruption that formed the Kilauea Iki Lava Lake. Part of the spatter cone had collapsed, revealing interfingered layers of reddish tephra and black lava flows. The tephra was erupted during episodes of Strombolian activity (lower effusion rates), and the lava flows were produced by fire fountaining (higher effusion rates). The lava flows formed the Kilauea Iki Lava Lake; much of the tephra was blown to the other side of the vent by trade winds (Pele’s tears and hair from day 2). Some olivene phenocrysts were altered to iddingsite in an oxidizing environment.

We left the lava lake and began climbing the crater wall. Looking back, we saw the western flank of the spatter cone. Material ejected from the spatter cone had landed on the flank of the cone. Eventually, it began moving down the cone in an aa flow after exceeding a critical mass, creating slickenslides on the underlying rocks.