Volcano Watch — Kīlauea Iki's lava lake has finally crystallized

The bottom, sides, and top of the lake were quickly encrusted as the lava chilled. But the center cooled slowly, owing to the lake's great thickness. At last, however, hard times have fallen upon the lava lake quite literally, as its vestiges of melt have finally crystallized into rock.

Kīlauea Iki's lava lake has been likened to a magma chamber emplaced at the surface of the Earth. Scientists eager to learn more about the crystallization process drilled into the lake several times. Core samples were obtained in 1960-62, 1967, 1975, 1976, 1979, 1981, and 1988. These experiments also yielded precise information about the rate of cooling.

Perhaps surprising to many is the slow pace of cooling for a large lava lake. One way to illustrate the cooling process is to track, through time, the depth at which a particular temperature is encountered. A useful temperature for discussion is 1,065 degrees C (1,950 degrees F), the temperature at which molten rock near the Earth's surface has largely crystallized. In the case of Kīlauea Iki, that temperature lay only 6.8 m deep (22.4 ft) in September 1960, nearly one year after the lake formed. As cooling proceeded, the distance to that temperature deepened-to 13 m (42 ft) in June 1962 and to 58 m (190 ft) by 1981.

Another way to track these changes is to monitor the growth in thickness of the lake's crust. In the initial drilling episodes, a sharp interface separated the upper crust from underlying melt. The upper crust thickened at a rate of 1.2 m (4 ft) per month in the first few months, slowing to about 0.1 m (0.34 ft) per month by December 1962, when the crust was 13 m (43 ft) thick. Five years later, in 1967, the thickness of rigid upper crust was about 27 m (87 ft). In 1975 the lake's crust was 55 m (180 ft) thick.

By 1981, the melt as a separate layer was gone. No extremely liquid-rich pockets or layers were encountered. Nevertheless, partially molten lava still filled the voids within the mesh of crystals in the cooling lava. It was still possible to recognize an approximate boundary, at a depth of about 60 m (198 ft), separating solidified crust from underlying, more plastic material.

The best guess for the year of complete crystallization is 1995, or about 35 years after the lake was emplaced. This estimate arises from a theoretical understanding of how heat is dissipated by conduction and convection. Maximum temperature in the core of the lake would still have been above 1,000 degrees C (1,830 degrees F).

And how hot is the core of the lake today? No precise measurements have been gathered since 1988. The question is difficult to answer even theoretically, because the cooling process changes as the lake solidifies completely. Fractures advance inward from the upper and lower surfaces, stopped only by a region of partial melt, which doesn't fracture readily. Once the lake's core has cooled below about 1,000 degrees C (1,830 degrees F), the fractures finish their inward propagation and meet in the middle, allowing more rapid transfer of heat.

By the end of 2002, the lake probably cooled below 500oC (930 degrees F). That's the limit of orange incandescence. While still hot, the lake's core probably has lost its glow and would appear black to our eyes.

Hikers crossing the crust of Kīlauea Iki today can find numerous places where steam issues from cracks on the crater floor, a consequence of rainwater percolating down via the fractures and being converted to steam. Rock-hard times may have come to the lake, but there's still plenty of evidence for heat.

Volcano Activity Update

Mahalo to all those several thousand people who visited HVO during the open house on January 4; you contributed to a remarkably successful day, despite the weather.

Eruptive activity at the Pu`u `O`o vent of Kīlauea Volcano continued unabated during the past week. Lava flows through a tube system from the vent to the sea. Lava continues to enter the ocean and form lava deltas (benches). Only the West Highcastle delta stayed active for the entire week; the Highcastle and Wilipe`a deltas both shut down during the week. A substantial new flow tongue, visible on Pulama Pali last week, developed two branches that made it over Paliuli and are now spreading slowly across the coastal flat.

The West Highcastle lava delta has had several small collapses in the past week, and explosions have been common. The public should be aware that the ocean entry areas can collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary onto the lava deltas and benches. Even the intervening beaches are susceptible to large waves suddenly generated during delta collapse; these beaches should be avoided.

No earthquakes were reported felt on the island during the past week.

Mauna Loa is not erupting. The summit region continues to inflate, though the rate of inflation has slowed gradually during the past month or two. The earthquake activity is low, with only 2 earthquakes located in the summit area during the last seven days.