October 12, 2022  

Rebirth of Ko’olau Volcano

Figure 1. Photo of a young tuff cone created within the last 100 ky during the rejuvenation phase of Ko’olau Volcano, contemporaneous with Koko Crater and Diamond Head.

These volcanic rocks were erupted more than 1.7 million years after the devastating collapse of the Ko’olau Caldera. It was probably a last gasp to release pressure within the magma chamber. Exact dating of these younger tuff cones is problematic, but they were all created within about a 50 ky window.

Figure 2. Map showing location of this post on Koko Head. The bay just above “Koko” is shown in Fig. 1. Koko Crater is just to the west.
Figure 3. Two islands, one constructed of lighter volcanic material (background), and one of darker in the foreground. I wonder if the larger is a remnant of the original Ko’olau caldera, a conjecture I can’t address with the data I have. The lighter color could be due to a different degree of alteration.
Figure 4. Blocks taken from the road cut seen in Fig. 1, showing similar vesicular basalt as observed at Koko Crater. However, there seems to be a lot less ash at this location, possibly because these rocks originated from lower in the volcanic cone.

The kinds of volcanic tephra produced by the original Ko’olau volcano and the younger tuff cones shows a tendency towards more ash and less basalt. Certainly, Koko, Diamond Head, and this unnamed crater were part of monogenetic fields. These cones degassed a part of the magma chamber then became dormant; others appeared to perform the same function in another part of the chamber, part of the overall development of the Ko’olau volcano.

With the extinction of the fires here and at Koko Crater, it is safe to say that Ko’olau is dead and the goddess Pele has moved to her new home in the Kilauea volcano, on Hawaii…

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