as the earth revolves, it gets either sunnier or darker. the darker time is when sunset occurs; the South Pacific is near the equator. the sun hits directly at the equator, so spots that are located on the equator are HOT.
to answer your question, (I am only ten!!! don't get mad if I'm wrong! :]) I would say that the sunset is because of the ashes. they probably rose into the air, making it change color. This happened to CA, as well, because three cities surrounding another city all caught on fire. we had lots of ash and bright, beautiful sunsets for a few days/weeks. if you have some fog, it is to help clear the ashes.
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