Day 1:  September 5, 2005

Reporting:

Danny Brothers, Emma Arnold, Brooke Eustis

Departure point. Calibrated GPS handheld unit to 4000’ (true to benchmark).

Stopped at overlook of Kilauea Caldera rim to view Mauna Loa to North and Kilauea Caldera to South. The Caldera rim is ~150 m above the caldera floor and is the point of highest relief. Notice dense vegetation to East of Kileuea Caldera and desert to the West. Several different flows are visible from this vantage point including the 1885, 1924, 1971, 1974, and 1982 events as well as Kilauea Iki, Pu’u Pua’I, and Halema’uma’u Crater. The different aged flows are differentiable by color; darker being younger and lighter being older. The caldera walls are older than the floor material. Steam vents and fumaroles are visible within caldera.

Looking to the North at Mauna Loa, distinguishing features are a smooth profile with vents and eruptives scattered along the profile.

While walking along the Rim Trail, notice the rim parallel extensional cracks and fissures as well as talus at the caldera floor. In several locations the cracks are filled or bridged by younger pyroclastic material.

At this stop we discussed the different types of ash deposits within the Keanakakoi member. The Keanakakoi member is composed of pyroclastic deposits with each layer representing a distinct event. The events took place from 1500-1790 and most likely were due to water coming into contact with the underlying magma or very hot rock (causing explosive eruption). Within the Keanakakoi member visible here, there is ash (< 2 mm), Lapilli (2-64 mm), and blocks/bombs (>64 mm). Further classification includes lithic (rock fragments), crystal (mineral form) and vitric (glassy nature). Pyroclastic deposits vary in terms of matrix support versus clastic support. Also, notice cross bedding, block sags and planar lamination at this location.

Here, we observed a crack hypothesized to have formed during a massive (M7.9) earthquake in 1868. The crack exposes the Keanakakoi member. Evidence for a 1971 fissure eruption is shown by pahoehoe lava on the upper edge of the crack. Moving away from the crack the lava graded from highly consolidated flow to less consolidated lithics. The lava appears to have spewed out and then flowed back into the crack.

This site is the origin of the SW Rift zone and is ~20 m deep, ~5 m wide with near vertical walls. It is thought that the crack filled with lava then was drained. The top edges are capped by ~ 10 cm of lava where blocks of the cap rock slid down the edge into the crack, leaving slickensides in the underlying hot rock.

We dropped into a shallow canyon to observe the canyon walls coated with a crust of red, greenish-yellow and white material. The red is iron oxide/hematite, white is amorphous silica and the greenish-yellow is jerosite (potassium-iron-sulfate-hydrate). This area is interesting because it is similar to environments on Mars. The presence of jerosite indicates there is a very specific water balance because too much water will cause it to be unstable and too little will hinder formation. After crushing the crust material a field PH test gave a PH of 3, indicating the desert is actually chemical rather than moisture induced (precipitation is ~60”/yr).

Here we observed different aged lava flows where blocks (1924) help constrain the ages of the other flows.

Cracks in this area can be used to measure extension to the south. Kilauea can only expand towards the south because Mauna Loa is blocking expansion to the north. There are three important measurements to characterize cracks: azimuth, opening direction and opening width.

The crater was a molten lake from 1905-1924 then drained in 1924 allowing water to penetrate to greater depths and generate massive steam explosions. The caldera is ~800 m in diameter and has a magma reservoir 1-3 km beneath the surface. There are several active steam vents and yellow sulfur stains on the pre-caldera crater walls.

Young ridge-like lineament ~1 km long. Eruption of highly viscous bombs and lava with low productivity creates near vertical formations. Evidence for near vent deposition is the absence of pumice and quenched surfaces between bombs. The frothy rock agglutinates were black and red (rapid oxidation). Certain rock fragments had a glassy iridescence created by thin film refraction. Looking NE, viewed in cross-section along the caldera wall is the Uwekahuna Laccolith, a precaldera intrusion.

These 5-8m high mounds were formed by pressure from magma intrusions. As magma pushes upward in the mounds V-shaped cracks form and expand as the lava degasses. The cracks range from a few centimeters to ~1 meter in width. Tumuli can form in very short time spans (less than 1 day).