The type of volcanic activity that visitors to Kilauea most often see is lava flowing into the ocean, and maybe a surface flow or two near the ocean entry. But where is this lava coming from? The source of current eruptive activity is Pu'u 'O'o, about 7 miles to the northwest and 2500 feet above sea level. So if magma is erupting that far away, how come you can't see a glowing river of lava for miles, all the way downhill to the ocean? Sometimes there are brilliant surface channel flows that go for several hundred yards, even miles, but these flows tend to solidify and stop after a few days - or do they?

Most of the time, the lava supplying the ocean entry is transported underground from Pu'u 'O'o, 7 miles downhill, all the way to its destination in the ocean. These underground channels are called "lava tubes". The physics of flowing lava dictate the formation of tubes: as lava flows along the surface of the ground, it cools inward from the outside. As the outside hardens, the thickening solid rock provides more and more insulation from the outside air. Relatively quickly, a stable cylindrical tube forms, and as long as the lava supply continues at roughly the same rate, a steady state is reached. The activity can remain in this state for weeks or years, until there is a pause or surge in eruptive activity.

Sometimes the ground above a lava tube collapses, forming what is called a "skylight". Skylights are important observation points for vulcanologists to study what is going on within a lava tube. They are also spectacular for the casual observer! Imagine walking through a field of solid black rock. Up ahead you notice the shimmer of heat just above a spot on the ground, blurring the scene behind it. You walk towards it. As you get close, the wind suddenly blows toward you and you feel an intense blast of hot air on your face, causing you to look back for fear of getting burned. The wind shifts away again, and you slowly walk towards the heat source. It's a hole in the ground, several meters wide, and there is a distinct orange glow coming from within. You look over the edge, and... well, it's pretty amazing!

A brilliant, smooth, bright orange river of lava whisks by. This stuff is really moving! It emits almost no sound. The ground below you is really hot - your hands might burn if you touched it without gloves. Suddenly you realize that you are standing on thin ground, and that this skylight is in fact the result of the collapse of this thin ground. You shudder with a vision of falling into the lava, and look around nervously. There are cracks in the ground about a foot or two from the skylight edges - better stay on the safe side of those cracks! You back up until you feel a bit more comfortable, but can still see into the skylight, and then you just gaze...