OUGS Walton Hall Branch Field Trip to the Hawai’ian Islands (Part 4) 11th May - 23rd May 2014

Led/Supported by:

Professor David Rothery, Professor of Planetary Geosciences at the Open University Dr Scott Rowland, Specialist Researcher, Department of Geology and Geophysics, SOEST Dr Sarah Fagents, Researcher, Hawai’i Institute of Geophysics and Planetology (HIGP) Professor John Sinton, Emeritus, Department of Geology and Geophysics, SOEST Dr Peter Moughinis-Mark, Director and Researcher at HIGP

Introduction

This field trip was a major excursion organised by members of the OUGS, to visit the Hawai’ian Islands to study in some detail, the volcanic evolution of the Hawai’ian Island chain. The trip was planned jointly by Professor David Rothery, Dr Scott Rowland and Dr Sarah Fagents. It included visits to the islands of O’ahu, Maui and Hawai’i. A total of 25 OUGS members took part in the excursion.

This is the 4th part of the account of the trip. This part describes our visit to the Kilauea Volcano southwest and upper east rift zones on Hawai’i Big Island. Further parts will follow in future editions of the Geo-Log.

The Hawai’ian Island Chain

In the 1st part of this account, I gave an introduction to the Hawai’ian Island chain. This is repeated below.

The Hawai’ian Island chain is the result of linear tectonic movement of the Pacific Plate over the “Hawai’ian” hot spot, beneath the northern central Pacific Ocean. The resulting seamounts broke the sea surface and formed the islands of through to Kaua’i (Figure 1), but continue as a chain of submarine seamounts in a line northwestward towards Kamchatka and the Bering Sea. The hot spot is presently under the new seamount Lo’ihi, which is building to the southeast of Hawai’i Big Island.

Figure 1 The Hawai’ian Island Chain

The islands each appear as volcanic complexes. For example, Hawai’i Big Island has five different shield volcanoes (Kohala, Hualalai, , Mauna Kea and Kilauea). See Figure 2.

Figure 2 The volcanoes on Hawai’i Big Island

In a talk we were given at the University of Hawai’i, we learned that Hawai’ian Island formation seems to follow a uniform path. The corresponding volcanic stages are:

1. An early submarine (alkalic) pre-shield stage (e.g., Lo‘ihi), 2. The main sub-aerial (tholeiitic) shield building stage (e.g., Mauna Loa and Kilauea), 3. A post-shield (alkalic) “capping” stage (e.g., Hualalai and Mauna Kea), and 4. An erosional stage (e.g., Kohala), once it has moved completely off the hotspot.

The time span, from Kaua’i to Hawai’i Big Island is about 5 Ma. The ocean floor is at an average depth of 4 to 5 km. In the talk, speaker Dr Pete Moughinis-Mark suggested the intermittency of volcano formation is likely due to continuously bending conduits and jump-back cycles. Crustal thickness is of the order of 30 km. Interestingly, the Mauna Loa magma chamber (on Hawai’i Big Island) is above sea level! The islands develop “moat like” depressions around them, due to the weight of the volcano(s) on them. This probably assists in the constant “fall apart” events that occur. There is evidence of major avalanches and long run-out land slips into and across the depressions. When these occur they invariably cause huge tsunamis.

The subaerial shield building involves eruption of lavas from summit calderas, fissures and rift zones on the shield flanks. Lava can be delivered to the shield flanks and edges beneath the surface, by lava tubes and dykes. Only the islands of Maui and Hawai’i Big Island have volcanoes in the shield stage with well-defined rift zones (Figure 3).

Figure 3 Maui and Hawai’i Big Island

In the various styles of volcanism, pahoehoe flows are slow-moving <18 to 20 m3s-1 and tend to be long lived, while a’a’ flows are fast-moving <100 to 200 m3s-1 and tend to be short lived. These are what form the lava flows/fields of the main shields.

There are so called “rejuvenation” phases of explosive, phreatic volcanism (involving water interaction) that seem to occur some 0.8 Ma after the shield building phase has ended. These later phases of explosive vol- canism seem to occur off the rift axes and are not (apparently) related to any pre-existing structures of the shield volcanoes or the ocean crust. They are not yet fully understood.

During the sub-aerial shield building stage, lavas erupting at the surface are tholeiitic and contain little compositional contribution from the ocean floor through which they have passed.

Kilauea Volcano Rift Zones - Hawai’i Big Island

After arriving on Big Island (16th), we drove up Volcano Road to the Kilauea Military Camp (KMC) where we were accommodated for the next three nights. After breakfast each day, Dr Sarah Fagents set out the plan for the day.

The following day (Saturday, 17 May), we visited several locations around the summit of Kilauea. This was a full and memorable day in our lives, described in some detail in the March 2016 edition of the Geo-Log.

On the days of 18th, 19th and 20th we spent time studying the rift zones of Kilauea. The SW rift zone has formed adjacent to the eastern flank of Mauna Loa and has produced occasional eruptions during the past three centuries. It is significantly buttressed by Mauna Loa. The Kilauea east rift zone, relatively unsupported, has seen many more eruptive events over this same time span.

Kilauea and Mauna Loa SW Rift Zones, Dr Sarah Fagents (Sunday, 18 May)

The SW rift zones of Kilauea and Mauna Loa volcanoes are shown in Figure 4.

Figure 4 Kilauea and Mauna Loa Rift Zones Modified from USGS downloadable map HI_Hawaii_349916_1975_250000_geo

After a good KMC breakfast, we set off SW along the Hawai’i Belt Road (highway 11), down to the coast at Honu’apo.

Along the way, past the town of Pahala, Sarah pointed out some low, elongate, flat-topped hills, up-slope, on the right. These are the Ninole Hills consisting of the “Ninole Basalt”. The Ninole Hills are actually on the southern flank of the Mauna Loa SW rift zone. Interestingly, the Ninole Basalt is found to be much older (0.1 to 0.3 Ma old) than all of the lavas so far studied from Mauna Loa, which are < 400 ka in age. The Ninole Hills are not well understood and thought to be (perhaps) the earliest lavas from Mauna Loa, or maybe the eroded shield remnants of an earlier volcano (Figure 5).

Figure 5 Ninole Hills

Sunday 18th, Location 1 – Honu’apo

When we reached the coast at Honu’apo Bay, we stopped at Whittington Beach Park. We walked through the park to the sea shore, and what remains of an old wharf. This is a good region to see the Pahala Ash deposit, which is an accumulation of hydromagmatic deposits spread SW from Kilauea. This deposit forms rich agricultural soils and gave the region of Pahala its sugar cane growing history.

The Pahala Ash outcrops as low cliffs on the coast. Sarah gathered the group at the old cane wharf. From the wharf, looking back towards the shore, she pointed out interesting features such as old lava tubes and pahoehoe flows in the cliff. Dave Rothery climbed down from the wharf and clambered across to the exit of a small lava tube (Figure 6).

Figure 6 Small Lava Tube – Pahala Ash, Honu’apo Bay

Some way off shore from here, the newest volcano of the Hawai’ian chain (Lo’ihi) is forming, developing a large sea mount. Lo’ihi is currently within 1 km of emergence, about 3 km above the ocean floor. After a brief stop at Honu’apo, we returned to the vehicles and continued on the Hawai’i Belt Road, down to South Point () on the southern tip of the island. South Point (incidentally) is the southernmost point of the USA.

Sunday 18th, Location 2 – South Point

South Point is out on a wide area of land south of the Hawai’i Belt Road. It is thought that the ancient Polynesians first arrived here, from Tahiti. In this region, in 1868, a disastrous sequence of earthquakes, tsunamis, landslides and eruptions took place, which took the lives of scores of people. The eruptions, from Mauna Loa SE rift zone, spread over a wide area and formed littoral cones at points where flows entered the sea (Figure 7).

Figure 7 Mauna Loa Lava Flow, 1868 – Littoral Cone

We stopped at the 1868 lava field and studied the terrain (Figure 8). The 1868 lava flow is an a’a’ lava that erupted quickly, at a rate of about 100 m3s-1. It erupted from a vent low on the flank of Mauna Loa. Lavas from low level flank vents frequently bring out accumulates from lower levels in the magma chamber. In this case, olivine crystals in abundance.

Figure 8 Mauna Loa Lava Field, 1868 – South Point (Ka Lae)

When the lavas reach water and form littoral cones, the fragmentation that occurs can expose the lava to rapid weathering. This releases the crystals from the groundmass, in huge quantities. Along the coast, at Papakolea Beach, the olivine crystals have collected to form an entire beach. Sadly we did not have time to visit this location.

South Point was our last geological location for the day. We had seen and heard much about the Kilauea and Mauna Loa SW rift zones, indeed about the Hawai’ian rift zones in general. Sarah suggested we all take some R&R (before studying the Kilauea E rift zone) by spending the rest of the day at Black Sand Beach.

Sunday 18th, Location 3 – Black Sand Beach (Punalu’u)

Black Sand Beach (more correctly, Punalu’u Beach Park) is a beach resort on the SE coast, between Honu’apo and Pahala. Green sea turtles bask and feed here. We spent a very pleasant interlude here, relaxing and swimming with the turtles (Figure 9).

Figure 9 Green Sea Turtle on Black Sand Beach

The black sand is basically basalt glass grains, from lava flows chilling and shattering on reaching the sea. Today, black sand beaches are present only on Big Island, built by waves and sea currents in particular lo- cations such as Punalu’u. This was our final location of the day.

Kilauea Upper East Rift Zone, Dr Sarah Fagents (Monday, 19 May)

Our next three days were spent studying the east rift zone. The upper east rift zone is shown in Figure 10.

Figure 10 Kilauea East Rift Zone

Modified from HVO USGS website gallery, Kilauea upper erz Acknowledgement to U.S. Department of Interior, U.S. Geological Survey.

Monday 19th, Location 1 – Puhimau Crater

Monday morning (19th), we set out on the Chain of Craters road to look at features on the Kilauea upper east rift zone. At our first location, Puhimau Crater, Sarah gave us an introduction to the dynamics of the east rift zone.

The upper E rift zone is characterised by features on the rift axis called “collapse craters” or “pit craters”. Puhimau Crater is a notable example. In the third part of this account, I had described how magma is transported (at depth) from the summit conduit, through dykes along the rift axes, to feed vents and fissures lower down the rift axes. In the Kilauea upper east rift, a feeder dyke (or conduit) had passed near to the surface. Its presence is indicated by the line of pit craters. Two mechanisms are proposed for formation of the pit craters:

1. A void forms above the dyke at depth, into which the roof falls. Successive collapses occur into the void. The void propagates upward through the poorly consolidated lava flows and appears at the surface as a pit crater (Walker 1988). Lava can sometimes erupt from and pond in them (e.g. Puhimau Crater).

2. Another theory (Okubo and Martel 1998) proposes that a pair of planar fractures extend upward from the top edge of the dyke in a V-like pattern and appear at the surface as a pair of cracks following the course of the dyke. Where the dyke is shallow, the cracks are closer together. Where the dyke is shallow, the smaller ‘V’ wedge can fall in and break up, forming pit craters. The “Devils Throat” is an example of this.

Sarah went on to say that the east rift keeps expanding. Seismic signatures coincide nicely with ground heave and rift widening events.

Monday 19th, Location 2 – “Devils Throat”

The “Devils Throat” is reached by a short trail through the forest, from a stop on the Chain of Craters road. The “Devils Throat” is an awesome sight (Figure 11).

Figure 11 Devils Throat

It was here that Sarah described the first time the “Devils Throat” was entered, in 1923, by geologist William Sinclair. At this time, the “Devils Throat” had an opening just about 10m wide. Sinclair was lowered on a rope by colleagues into the opening. He noted that the walls were not vertical but sloped away from him, into blackness. He was in a void of immeasurable depth and width and his colleagues were standing on an overhang over the void(!). Later, the crater was found to have the shape of an inverted funnel, a depth of about 78 m and a width (long diameter) of about 60 m. In the years since, the walls have collapsed and partially filled the crater. It is now just about 50 m wide and about 50 m deep. We were warned to keep back from the edge(!).

On the return to the road, Sarah pointed out the extensive surface cracks (not obviously aligned to the rift axis), that had caused repeated buckling of the Chain of Craters road surface. Further down the Chain of Craters road, we came upon the start of the Napau Trail.

Monday 19th, Location 3 – Napau Trail

The Napau Trail gives access to the recently active vent of Mauna Ulu, strongly active from 1969 to 1974. From the trailhead, we set out westward to the Mauna Ulu lava field, then turned southward (downslope). In a couple of minutes, we reached the end of a splendid east-west eruption fissure, possibly up to 1 km in length. This was shadowed along much of its length (on the north side only) by a superb spatter rampart some 6-8 m high (Figure 12).

Figure 12 Eruption Fissure with Spatter Rampart (Mauna Ulu 1969 eruption)

Lava erupted here (in 1969) had fountained and fallen to both sides of the fissure, but rapid lava delivery had swept away all air-fall lava south of the fissure. The area had been thickly forested before the eruption and there remained the boles of many trees, now burned out, but keeping the pear-drop shaped hollow in the centre of a lava cloak. Interestingly, trees of sufficient girth to remain in place while the lava cooled, had retained a lava “collar” just about 1.5 m (guessed) above the original land surface height (Figure 13).

Figure 13 Tree Stump, cloaked in Lava

Sadly, the weather was not good (raining) while we walked the fissure, but improved greatly after we set off on the Napau Crater Trail for the summit of Mauna Ulu. Monday 19th, Location 4 – Mauna Ulu Summit

As we crossed the pahoehoe lava field towards Mauna Ulu summit, Sarah pointed out where a previous crater had been infilled by lava from the 1969 eruption. Little could be discerned of the previous crater in the topography. We also learned of the Hawai’ian term “kipuka”, meaning an ‘island’ of ground (usually higher ground) that was surrounded by a young lava flow but itself escaped inundation. We had a picnic lunch at the summit of Mauna Ulu (Figure 14) and surveyed the surrounding landscape, including the location of the now in-filled Alae Crater. The landscape was steaming in places, after the recent rain.

Figure 14 Mauna Ulu Summit Caldera

After lunch we returned along the trail back to the vehicles. The eruption at Mauna Ulu began in May 1969, beginning with seven months of high fountaining from the Mauna Ulu vent, followed by a longer period of effusive eruptions from fissures like the one we had seen earlier. A vent opened briefly in the Kilauea summit caldera. Eruptions continued until late 1971. In 1972, eruptions from Mauna Ulu began again and continued until July 1974.

We returned to the vehicles and headed south down the Chain of Craters road, to the edge of the Hilina Pali. The road snakes its way southeast, downward over the Mauna Ulu lava flows. The Hilina Pali cliffs are the surface expression of a system of deep, gently active faults that run for 15 km along the southern flank of Kilauea volcano. As Kilauea gradually splits apart along the rift zones, slips occur along the Hilina Pali fault lines and the cliffs grow ever higher.

Monday 19th, Location 5 – Kealakomo Lookout Platform - Hilina Pali

We stopped at a point on the road above the Hilina Pali cliffs called Kealakomo. Here, there is a look-out platform from which one can view the extent of the Mauna Ulu lava field, and a considerable length of the coastline (Figure 15).

Figure 15 Kealakomo Lookout Platform

We stopped at Kealakomo for a while to take in the view. There was much to see. But all too soon, we had to continue down the snaking Chain of Craters road to the coast.

At the coast, the road swings east towards Kalapana. But after 4 km or so, the road is blocked where is was overrun by the 2002-2004 pahoehoe lava flow from Pu’u ’O’o Crater. Actually, the road is closed at a point about 1 km short of the lava flow. To see the lava on the road, one must walk the additional kilometre (Figure 16).

Figure 16 Pu’u ’O’o lava flow (2002-2004), blocking the Chain of Craters road

The Pu’u ’O’o lava flow on the Chain of Craters road was the final location of the day, and also the final location in our study of the Kilauea upper east rift zone. Our next two days were spent studying the Kilauea lower east rift zone and the Saddle Road to Kona. To be covered in our next Geo-Log.

Tom Miller