Category Archives: Geology

Petrologic Monitoring of Kilauea Volcano

Geology,

The summit eruption at Kilauea volcano has provided geologists with a unique opportunity to see into the underground plumbing structure of Kilauea. It was long debated, for example, whether there was a direct connection between the shallow magma chamber below Kilauea’s summit and the Pu’u ‘O’o vent on the East Rift Zone. Also, was the lava in the lava lake at Halema’uma’u the same lava that erupted at the summit in 1982?

Chemically, it seems the lava  that is erupting at Pu’u ‘O’o is the same lava that is erupting at the Halema’uma’u vent. The only difference between the lavas is in the crystallization of minerals in the lava. The lava at Halema’uma’u is very, very hot (2,140 degrees Fahrenheit) with only small-sized olivine crystals within the lava. The lava at Pu’u ‘O’o is slightly cooler (2,100 degrees Fahrenheit) and contains a greater diversity of crystals, including olivine and pyrozene. While both minerals exist in Hawaiian lavas, they crystallize at different temperatures.

The presence of these crystals suggest a complicated system of magma recharging beneath Kilauea, with the lava erupting being a mix of gas-rich, crystal-less newer magma and older magma that had already partially crystallized in Kilauea’s magma chamber.

A recent article from the Hawaiian Volcano Observatory’s Volcano Watch column explains this process and mystery much better than I ever could. It’s an interesting read for anyone interested in petrology and Kilauea’s internal plumbing system in general.

Caves of Hawaii part 1

Geology, Hawaii, History, , ,
(Photo from the Bishop Museum’s collections)

Beneath Manoa, there exists a huge but relatively unknown system of underground caves and water caverns centered roughly at the intersection of University Avenue and King Street.

Well, at least the system used to be huge. During the 1920s, the cave system stretched at least as far north as the University of Hawaii’s upper campus, and at least as far south as Kapiolani Boulevard, and prior to that the system was probably even more extensive.

It was a very beautiful system. Water from these caves fed springs that in turn fed beautiful ponds. These ponds were prized by Manoa residents for their clean water and beautiful fish.

Today, some of the caves are still there (most notably the Moiliili Water Cave beneath University Avenue), but much of the system was destroyed as Honolulu urbanized.

The greatest damage to the system was done in 1934, when a construction project downslope of the cave system struck the caverns, causing much of the water in the caves to drain before the leak was sealed. The result was nothing short of an economic disaster. The caves’ water spewed from sidewalks, houses and trees sank, and water and gas lines ruptured.

As the water level dropped, the ponds of Manoa disappeared almost immediately (along with most of their fish). The loss of water caused the land in Moiliili to become unstable, and sinkholes appeared in many areas. In one instance, an entire store collapsed into a sinkhole. Interestingly, investigators saw some of the fish that disappeared from the former ponds swimming inside that particular sinkhole.

As urbanization increased, many parts of the old cave system were destroyed or filled in. For example, it is unknown whether the portion of the cave system underneath the University of Hawaii’s upper and lower campuses still exist. Today, only one of these caves remains readily accessible: the Moiliili Water Cave.

Interestingly, aside from some construction fill, the Moiliili Water Cave beneath University Avenue is surprisingly unpolluted (its bacteria counts have actually been on the decline in recent years, and is apparently significantly lower than, say, Manoa Stream), its water crystal-clear and its water very cool to the touch. In fact, fish still swim in the cave’s waters. This cave is the only known remaining portion of the old cave system today (though other parts of the cave system, near where the Stan Sheriff Center now stands, were known to exist as recently as 1979, complete with a whole pond full of catfish in one part of the cave; however, it is unknown whether these caves were destroyed during the development of UH’s current athletic complex and lower campus parking lot), and it should be preserved and protected in the interests of future generations and history fanatics like me.

MODERN CONNECTION: Many people were alarmed when, this past June, the city released this photo of what a rail system passing through Moiliili would look like. Many people wondered why they couldn’t just stick the rail system underground like how they’re proposing to do it in downtown Honolulu. The main reason why they can’t stick the railroad underground in Moiliili is because of the underground caverns in the area–that is, a subway tunnel in the area would 1) destroy the cave system (though I doubt the city cared about that), 2) would likely be flooded due to the low water table in the area, and 3) would just be too expensive.