Geologic Map of Kalaupapa Peninsula, Moloka‘i, Hawai‘i, USA

Abstract

Kalaupapa Peninsula, along the northern coast of East Moloka‘i volcano, is a remarkably well-preserved example of rejuvenated-stage volcanism from a Hawaiian volcano. Mapping of lava flows, vents and other volcanic constructs reveals a diversity of landforms on this small monogenetic basaltic shield. The late-stage lava distributary system of this shield is dominated by a prominent lava channel and tube system emanating from the primary vent, Kauhakō crater. This system, along with several smaller examples, fed five prominent rootless vents downslope from Kauhakō. This map shows the subaerial part of this volcanic construct at 1:30,000 scale and encompasses an area of approximately 20.6 km².

Keywords:

• Kalaupapa
• Hawai‘i
• volcanism
• lava tube

1. Introduction

This work was authored as part of the Contributor's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 USC. 105, no copyright protection is available for such works under US Law

This work adds detail to previous geologic mapping efforts of Kalaupapa Peninsula (e.g. Coombs, Hawke, & Wilson, 1990; Stearns & Macdonald, 1947) by delineating individual lava flows and related geologic structures, such as lava channels, collapse features, and other volcanic constructs. The Kalaupapa Peninsula is located along the northern coast of the island of Moloka‘i, State of Hawai‘i, USA. The subaerial morphology of Kalaupapa Peninsula is largely defined by Pu‘u ‘Uao, a monogenetic shield formed during rejuvenated-stage activity of East Moloka‘i volcano (Walker, 1990). The summit region of Pu‘u ‘Uao is punctuated by Kauhakō crater, which presently contains a meromictic alkaline lake (e.g. Donachie, Bidigare, Sadler, & Karl, 1999).

The radiometric ages (K-Ar) and 1σ analytical errors for the Pu‘u ‘Uao flows fall within the range of 0.344 ± 0.031 Ma to 0.570 ± 0.025 Ma (late Pleistocene) (Clague et al., 1982). The other units in the Kalaupapa Volcanics have not been dated.

After cessation of volcanic activity, fans consisting of talus and alluvium derived from the East Moloka‘i Volcanics encroached onto the newly formed peninsula. These deposits form marine terraces graded to the ∼8-m Waimanalo stand of the sea (Stearns & Macdonald, 1947), which occurred during the late Pleistocene (0.11 to 0.13 Ma; e.g. Muhs, 2002).

The purpose of this mapping is to document the styles of volcanism preserved on Kalaupapa Peninsula, which has received little attention in previous geologic studies of the area despite being an important archeological site. The map area is within the US Geological Survey's 1:30,000 scale Kaunakakai quadrangle (U.S. Geological Survey, 1993).

2. Methods

A base map of the field area was first constructed using orthorectified aerial photographs as a base layer, with overlays of digital line graph representations of hydrography, topography, and roads. The aerial photographs were from US Department of Agriculture aerial surveys conducted in 1965. The digital line graph data were from the US Geological Survey and were produced from the 7.5-minute Kaunakakai quadrangle (U.S. Geological Survey, 1993). Field mapping was conducted using 1:6,000-scale printouts of the base map. Units were mapped on the basis of surface texture and composition, lava flow margins, and stratigraphic relations. Global positioning system measurements using a handheld receiver were taken to verify the locations of mapped features such as flow boundaries, crater rims, ridges and troughs. Hawaiian geographic names were assigned based on historic maps and discussions with residents of Kalaupapa town.

3. Discussion

The oldest unit in the map area is the lower member of the East Moloka‘i Volcanics (Qem), which forms cliffs exceeding 500 m in elevation along the southern border of the map. This unit is characterized by ‘a‘ā and pāhoehoe, with interbedded pyroclastic deposits, and it includes crosscutting dikes. These volcanic rocks were emplaced during the shield-building stage of East Moloka‘i volcano and then exposed as the headwall cliffs of a large landslide from the volcano's north flank (Clague & Moore, 2002).

The Kalaupapa Volcanics encompasses all of the volcanic units exposed on the peninsula. The basal flow unit (Qkbf) contains the oldest subaerially exposed rocks of the Kalaupapa Volcanics and consists entirely of ‘a’ā lava flows. At most, a 15-m-thick vertical section through these flows is subaerially exposed in wave-cut terraces and cliffs along the present shoreline. A weathering horizon is not observed between the basal flows and the overlying Pu‘u ‘Uao flows, or between any other flow units of the Kalaupapa Volcanics. The source of the basal flows is not exposed, and rocks that resemble these flows (‘a’ā) are not observed within the walls of Kauhakō crater. Pu‘u ‘Uao is a likely source however, due to the lack of a weathering horizon on top of the basal flows (suggesting a similar age with the rest of the Kalaupapa Volcanics) and because the basal flows are exposed to the east and west of Pu‘u ‘Uao.

Eruption of the Pu‘u ‘Uao flows (Qkpo) followed emplacement of the basal flows in the Kalaupapa Volcanics. The Pu‘u ‘Uao flows and younger flows on Kalaupapa Peninsula erupted from Kauhakō crater. Spatter and frothy pāhoehoe are exposed in the walls and rim surrounding Kauhakō, indicating significant magma degassing. Stacks of numerous thin pāhoehoe flows, approximately 4 cm in individual thickness, as well as shelly pāhoehoe are exposed in the walls of Kauhakō, whereas flows several hundred meters or more away from the crater are thicker (∼1 m or more) and less vesicular.

A chain of eight closely spaced, overlapping pits extends north from within the northeast rim of Kauhakō crater, each pit being an elongate scallop-sided depression. The line of the pits is roughly tangential to the eastern margin of the crater. The third and fourth pits (numbered on map) are separated by a 40-m-wide septum. The depression formed by the first three pits embays the northeast rim of Kauhakō crater. All of the pits have funnel shape and are circular to elliptical in plain view. The pits are 15- to 25-m deep and 75 to 100 m in diameter. Pit walls are steep and covered by talus, and low septa of talus separate individual pits. Neither ponded lava nor sections of preserved lava tube or dike are observed within the pits. Whereas the origin of these pits is poorly constrained by field observations, formation by collapse above a lava tube is most likely.

Two northeast-trending troughs begin along the east flank of the pit chain. The northernmost trough leads downslope to a series of closed collapse depressions, lava tube skylights, and a small volcanic construct (‘lava rise 2’). The southernmost trough reaches nearly to the coast. These troughs are interpreted as channelized pāhoehoe flows, which develop into lava tubes further downslope.

A prominent lava channel, 30 to 70-m wide and 4 to 8-m deep, originates from the northernmost pit from Kauhakō crater. This channel trends 015° (measured clockwise from north) for 220 m, then turns sharply to 320°. A broad ridge trending 010° originates at this bend in the lava channel and slopes down to the north. This ridge may be a lava tube or filled lava channel. Past the bend, the channel extends for an additional 300 m before terminating at a 12-m deep, 8-m wide and 3-m-high lava tube cave. The soil-covered floor of the cave is flat and the roof of the cave slopes down to the northwest. Details of this and other caves on Kalaupapa Peninsula are discussed in detail elsewhere (see Thornberry-Ehrlich, 2010 and references therein).

Four volcanic constructs have been identified northeast of this lava tube cave, and each construct is associated with a mapped flow unit. These are, from south to north, lava rise 1 (Qkr1), Makapulapai (Qkmo, Qkmy), Kapapakikane (Qkka), and Ki‘ikolu (Qkki). There are no structural indications of a feeder dike underlying these four constructs, such as fractures, faults or graben, although such evidence may have been buried. These constructs are aligned along the general northwest trend of the lava channel and tube that extends downslope from Kauhakō.

The southernmost volcanic construct, lava rise 1, is roughly 160 m in diameter, with sub-horizontal lower flanks that lead up to an increasingly steep summit (∼15°–20° slopes). The summit is capped by a large hornito. A depression 35 by 50-m wide and 10 to 15-m deep, occurs immediately to the northwest of the summit. The interior of this depression is covered by talus, but the walls are lined with lava stalactites and other lava dripstone features. These features indicate that the depression formed through collapse of a drained lava tube or tumulus below its summit hornito. Areas along the depression walls not covered by dripstone reveal a cross section through outwardly dipping pāhoehoe flows that have thicknesses of tens of centimeters to more than a meter. There is also a lava tube skylight on the northwest flank of this construct, approximately 10-m northwest of the rim of the summit depression.

Farther northwest (and downslope) is Makapulapai. Makapulapai has steep to nearly vertical sides covered by large angular blocks 1 m or more in width. The top of Makapulapai is nearly flat and bordered by a 2–3-m wide and 1–2-m deep circumferential cleft. Exposures of the flows within this cleft indicate that at least the final phase of activity here was largely inflationary in nature and that Makapulapai is a large tumulus. Pāhoehoe emanated from the site of Makapulapai and flowed to the east (Qkmo) and then to the west (Qkmy).

Kapapakikane, a small lava shield, lies to the northwest of Makapulapai. This shield has a summit depression that is ∼15 m in diameter and ∼7-m deep. The summit depression is covered by wall rock-derived talus. Massive pāhoehoe flows dip radially away from the rim of the summit. A small portion of a lava tube is exposed in the south wall of the summit depression.

The northernmost construct is Ki‘ikolu, another small lava shield. Its summit depression is 150 m in diameter and 10 to 12-m deep. Pāhoehoe flows dip radially away from the summit depression. Ki‘ikolu is the site of a historic US Coast Guard lighthouse and thus has been disturbed by heavy construction. Several alcoves that may be sections of lava tube have been backfilled and graded to the point where positive identification is not possible.

These observations point to a tube-fed origin for lava rise 1, Makapulapai, Kapapakikane, and Ki‘ikolu, rather than these constructs being primary vents fed by a subjacent dike. These four constructs are in line with, and downslope from the well-developed lava tube and channel system that emanates from Kauhakō crater. Lava tube skylights and caves are also exposed at or between most of these constructs. Further, the flows are thick and considerably degassed, like tube-fed flows, not thin and highly vesicular like those observed at Kauhakō crater. Accordingly, these constructs are interpreted to be rootless vents that were fed by lava erupted at Kauhakō crater and transported downslope through lava tubes and channels.

Makapulapai appears to be the youngest rootless vent in the Kalaupapa Volcanics. The stratigraphic relation between the three older rootless vents, Ki‘ikolu, and Kapapakikane, and lava rise 1 is unclear. The contact between Ki‘ikolu and Kapapakikane lavas is indistinct, and any possible stratigraphic contact with the lava rise 1 flows is buried by the Makapulapai flows. Both the younger and older Makapulapai flows are deflected around the slopes of Kapapakikane and lava rise 1.

The adjacent Pu‘u ‘Ula scoria cone, on the cliffs immediately southwest of Kauhakō crater, has not been radiometrically dated. It is thought to be a result of rejuvenated-stage volcanism at East Moloka‘i volcano (Coombs et al., 1990). The relative timing between eruptive activity at Pu‘u ‘Uao and Pu‘u ‘Ula is unknown. The location of Pu‘u ‘Ula shown this map was determined using a handheld global positioning system receiver in the field. UTM coordinates are 710206 m E, 2343297 m N, zone 4, NAD83.

4. Conclusion

The Kalaupapa Peninsula is a noteworthy example of rejuvenated-stage effusive volcanism along the north coast of East Moloka‘i volcano. Pu‘u ‘Uao, the principal volcanic construct on the peninsula, exhibits the classic geomorphology of a monogenetic basaltic shield. The late-stage lava distributary system of Pu‘u ‘Uao is remarkably preserved and shows a well-developed lava channel and tube system emanating from the primary vent, Kauhakō cater. This system fed effusive activity from at least five rootless vents further downslope.

Software

Digital scans of the aerial photographs were processed using Adobe Photoshop. Base maps used for field mapping were compiled in ESRI's ArcGIS. Geologic units were digitized from scans of annotated field maps using Adobe Illustrator. The layout of the map was also accomplished in Adobe Illustrator.

Acknowledgements

Careful and thorough reviews of this map by M. Dooley, S. Rowland, and an anonymous reviewer are sincerely appreciated. L. Kestay, J. Skinner, and J. Richie assisted with the USGS internal review of this publication (IP-037131). W. Halliday provided assistance in the field. This work was conducted under a scientific research permit granted by Kalaupapa National Historic Park.