Evidence for water influx from a caldera lake during the explosive hydromagmatic eruption of 1790, Kilauea volcano, Hawaii

Abstract

Abstract. In 1790 a major hydromagmatic eruption at the summit of Kilauea volcano, Hawaii, deposited up to 10 m of pyroclastic fall and surge deposits and killed several dozen Hawaiian natives who were crossing the island. Previous studies have hypothesized that the explosivity of this eruption was due to the influx of groundwater into the conduit and mixing of the groundwater with ascending magma. This study proposes that surface water, not groundwater, was the agent responsible for the explosiveness of the eruption. That is, a lake or pond may have existed in the caldera in 1790 and explosions may have taken place when magma ascended into the lake from below. That assertion is based on two lines of evidence: (1) high vesicularity (averaging 73% of more than 3000 lapilli) and high vesicle number density (105-107 cm -3 melt) of pumice clasts suggest that some phases of the eruption involved vigorous, sustained magma ascent; and (2) numerical calculations suggest that under most circumstances, hydrostatic pressure would not be sufficient to drive water into the eruptive conduit during vigorous magma ascent unless the water table were above the ground surface. These results are supported by historical data on the rate of infilling of the caldera floor during the early 1800s. When extrapolated back to 1790, they suggest that the caldera floor was below the water table.

Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i

“…1800 CE (Swanson et al, 2012a). The phreatomagmatic and phreatic nature of most of the explosive eruptions suggests that the two calderas were often deep, at or below the water table (Mastin, 1997;Mastin et al, 2004). Today the water table is ~615 m below the highest point on the caldera rim, ~490 m below the caldera fl oor (Keller et al, 1979).…”

Episodic thermal perturbations associated with groundwater flow: An example from Kilauea Volcano, Hawaii

“…Swanson, U.S. Geological Survey, oral communication, 2001] as a possible trigger for the onset of the hydrothermal plume (Figure 9). The large 1790 A.D. phreatomagmatic eruption [McPhie et al, 1990;Mastin, 1997], the 1868 M L 7.9 earthquake [Wyss, 1988] (Figure 1), which was the strongest historical earthquake in Hawaii, and the 1924 phreatic eruption [Jaggar and Finch, 1924] are apparently ruled out as Figure 9. Calculated time frame for the onset of the hydrothermal plume using initial temperature conditions represented by curve 1 (horizontal stripes) and curve 2 (vertical stripes) in Figure 4 and the chronology of major documented volcanic and faulting events in the region of Kilauea Volcano.…”

“…A permeability decrease at a particular depth horizon caused by lateral flow of hydrothermal fluid may later help to control the level of the water table within the edifice. The general effect of such episodes might be to elevate the water table position, thereby promoting the formation of summit crater lakes [Mastin, 1997] and enhancing the potential for phreatic eruptions.…”

Numerical model of crater lake eruptions

“…Numerical investigations of subaqueous volcanic eruptions have been limited to thermodynamic models that either calculate eruption energies and velocities for compressible fluids ranging from pure steam to hot rock and water mixtures (Mastin 1995) or simulate the effect of adding water to a one-dimensional eruption column (Koyaguchi and Woods 1996;Mastin 1997). These models demonstrate that when the mass fraction of water is slightly increased and the mass flux of magma that produces a Strombolian type of an eruption stays the same, the result is an increase in eruption energy and in plume height, and deposits that are considered dry due to the conversion of water to steam (Mastin 1995;Koyaguchi and Woods 1996).…”