Volcano Watch — Footprints in Ka`u were probably made in 1790—but not by Keoua's party

Barefoot walkers left thousands of footprints in wet volcanic ash within a few kilometers (miles) southwest of Kīlauea's summit. In 1921, Thomas Jaggar related the footprints, "discovered" the previous year, to survivors or rescuers of the 1790 eruption, mainly because he assumed that few people visited the supposedly kapu area except in 1790. Archaeologists from Hawai`i Volcanoes National Park recently questioned whether the footprints were made at that time and by warriors, citing a wide range of directions that people were walking and evidence of extensive human use of the area (see their report at http://www.nps.gov/havo/historyculture/footprints.htm).

As part of a study of Kīlauea's explosive past, we examined the footprints, the ash bed that contains most of them, and the relation of that ash to other explosive deposits.

Forensic studies indicate that the length of a human foot is about 15 percent of an individual's height. A man's foot may be slightly more that 15 percent, a woman's slightly less, but it is possible to estimate the height to a few centimeters (a couple of inches).

We measured 405 footprints to determine how tall the walkers were. A footprint is probably longer than a foot when made in muddy ash, so our height estimates may be slightly too tall. The average calculated height is only 1.5 m (4'11"), and few footprints were made by people 1.75 m (5'9") or more tall. Early Europeans described Hawaiian warriors as tall; one missionary estimated an average height of 178 cm (5'10"). Clearly, most of the footprints were made by women and children, not by men, much less warriors.

We traced the footprints-bearing ash bed from the national park's Footprints Area back to the southwest side of Kīlauea's caldera and found that it is one of the younger explosive deposits, but not the youngest. Its surface was dimpled by small rocks that fell into the ash while it was still wet. Several such rocks plopped into footprints, just after people walked across the ash.

The rocks fell during the early part of an explosive eruption that reached high into the jet stream. We know that, because the debris was dispersed mostly east-southeastward by a west wind, a direction found only at high altitudes in Hawai`i. Probably at the same time, surges of hot ash and gas swept over the southwest and west rims of the caldera; their deposits have been found covering the footprints ash. These relations indicate that the footprints ash was an early stage of a powerful eruption that had both a high column and dangerous surges.

Hawaiian oral tradition, and John Young's reported observation, say that the 1790 eruption was large, and Jaggar calculated a column height probably greater than 9 km (30,000 ft), based on its appearance as a "pillar" over Mauna Loa when viewed from Kawaihae. This is about halfway into the jet stream. Our work found two "jet-stream" deposits of the late 1700s strewn east of Kīlauea's summit. The younger probably formed in 1790.

A reconstruction of events suggests that wet ash, containing small pellets called accretionary lapilli, fell early in the eruption, blown southwestward into areas where family groups, mainly women and children, were chipping glass from old pahoehoe. They probably sought shelter while the ash was falling. Once the air cleared, they slogged across the muddy ash, leaving footprints in the 2-cm- (1-inch-) thick deposit.

Meanwhile, Keoua's party was camped on the upwind side of Kīlauea's summit—perhaps on Steaming Flat—waiting for Pele's anger to subside. They saw the sky clear after the ash eruption and began walking southwestward between today's HVO and Namakanipaio. Suddenly the most powerful part of the eruption began, developing a high column and sending surges at hurricane velocities across the path of the doomed troupe. Later, survivors and rescuers made no footprints in the once wet ash, which had dried.

If these observations and ideas are correct, the footprints were made in 1790, but not by members of Keoua's group. This conclusion should please everyone. Jaggar was right (but for the wrong reason) that the footprints were made in 1790, and park archaeologists are right that most of the prints weren't made by Keoua's party.

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Volcano Activity Update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala during periods of trade winds and communities adjacent to Hawai`i Volcanoes National Park during kona wind periods. There have been several small ash-emission events, lasting only minutes, in the last week. These are preceded by small seismic events, and are probably initiated by tiny rock falls within the vent. In addition, a small explosive eruption occurred from the vent in Halema`uma`u Crater at 7:37 a.m. on August 27, depositing hot ejecta onto the crater rim. This is the fifth explosive eruption since the vent opened in March.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo. Incandescence continues to be observed at night inside Pu`u `Ō`ō and suggests minor activity from vents within the crater.

Lava continues to erupt from fissure D of the July 21, 2007, eruption and flows toward the ocean through a well-established lava tube. Several small and short-lived breakouts on the coastal plain occurred on August 22 and 26, with both episodes related to changes in lava supply associated with deflation/inflation events at the summit. Lava continues to flow into the ocean at Waikupanaha, and has been typically producing a moderately vigorous plume. The aforementioned changes in lava supply have also led to brief fluctuations in plume vigor over the past week.

Be aware that lava deltas could collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions, as have been seen lately. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check Civil Defense Web site or call 961-8093 for viewing hours.

Mauna Loa is not erupting. No earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

Two earthquakes beneath Hawai`i Island was reported felt within the past week. A magnitude-2.6 earthquake occurred at 11:59 p.m., H.s.t., on Saturday, August 23, 2008, and was located 4 km (2 miles) southwest of `O`okala, at a depth of 11 km (7 miles). A magnitude-3.3 earthquake occurred at 1:52 a.m. on Thursday, August 28, 2008, and was located 1 km (1 mile) northeast of Ka`ena Point at a depth of 33 km (20 miles).

Visit our Web site for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. skip past bottom navigational bar