Sunday, June 26, 2016

The Hawai'i That Was: Pu'u O'o, the Volcano We Couldn't See

The Pu'u O'o cone from above Hilo
Disclaimer: This is NOT happening right now! These pictures are from 2009.

Pu'u O'o is the invisible volcano on the Big Island. It's been the center of eruptive activity for much of the last thirty years, but there are very few easily accessible localities from which it can be seen. One pretty much has to fly over it to see anything at all.

We are continuing a journey to understand the Hawai'i That Was, seeking to understand the islands as they were before European contact, and before Polynesians arrived a thousand years earlier. Understanding the islands requires an understanding of volcanism. The islands exist only because of lava, and in observing active eruptions we see the origins of each of the Hawaiian islands.
Getting closer to the Pu'u O'o cone. Notice the lack of surface flows of lava. It's almost all beneath the surface in lava tubes.
There is a huge unknown involved with every journey to the islands. The volcanoes refuse to follow a schedule, and feel no need to be convenient to the itineraries of visitors. It's true that Kilauea has been erupting continuously now for more than thirty years, so there is a fair chance that the eruption will continue for the foreseeable future. Then again, the eruption could end tomorrow. There's just no way to know. So, one plans for the possibility, but leaves a lot of alternate activities if lavas aren't visible anywhere.
The location of the lava tube system was obvious. Every so often the roof of the tube would collapse, forming a skylight that emitted steam and other gases.
Kilauea is the sole volcano erupting on the island right now, although Mauna Loa is showing a few hints of possible activity. The lavas are exposed at two localities, at Halemaumau in the Kilauea Caldera (see the previous post), and at the cone of Pu'u O'o on the east rift zone about ten miles away. During the many months that we were planning the trip, Pu'u O'o was pretty much just simmering with no active lava flows since 2014, when the town of Pahoa in the Puna District was briefly threatened (damage was thankfully limited).
So we had a hard decision to make: do we bust the budget on a helicopter flight in hopes of seeing lava flows, though there have been none for more than a year, or do we make other arrangements? We opted to make other choices, which was good because we arrived on the islands during a wet spell, and we probably would have seen little through the rain clouds, although a small lava flow started a week before we arrived. It's now three miles long and approaching the coastal pali (look here for a recent video), but we've been home for nearly two weeks. We just plain missed it.
Looking into the crater of Pu'u O'o, source of the lava flows
The situation was different in 2009, the last time we held a class on the islands. Pu'u O'o had been very active for more than a year, with a broad "delta" and lava tube system feeding basalt into the ocean. We opted for the helicopter flight and were richly rewarded. For one reason or another, I've never collected these pictures together in a blog post.
A rootless shield on the Pu'u O'o lava flow.
The first two photos above show the Pu'u O'o cone and crater from a distance. At various times it has been a more prominent cone, but at other times it collapses. Lava left the cone through a series of lava tubes and flowed southeast towards the coast. Sometimes lava would well up through a skylight, forming a small "rootless shield" like the one in the picture above.
I was surprised, almost disappointed by the lack of "rivers" of lava, but our pilot found a recent breakout, and we saw glowing lava and silvery pahoehoe flows that had formed only hours earlier.
Active lava flows on the slopes below Pu'u O'o. This would have been a real spectacle at night.
The silvery reflective appearance was caused by the formation of a thin film of volcanic glass on surface of the flow. The glass breaks off and degrades quickly, leaving behind the more characteristic dull black or dark gray surface.
A skylight over a lava tube.

If you are having trouble visualizing the scale, realize that we never dropped below 500 feet in altitude. The skylight above is probably 30-40 feet across.
Minutes-old breakouts
Our flight continued over the pali (cliff) and onto the coastal plain. Farther from the vent there were more kipukas, islands of forest that were spared from destruction as the lava flowed by. Kipukas are the seed repositories that would eventually cover these flows with new forests.
And then we reached the coast, where the lava emerged from the lava tubes and plunged into the sea. The union of hot lava and cold seawater was explosive. The lava shattered into black sand on contact.
Occasionally we could see lava through breaks in the clouds of steam.
We flew around, but not through the steam cloud. It is a noxious mix of hydrogen sulfide and acids.
As I went through the pictures much later, I found that one of them gave an end-on view of the entire eruption from Pu'u O'o on the right to the ocean entry on the left (below). The distance between is seven miles (11 kms). It's hard to describe the feeling of seeing the forces of creation and destruction at war with each other. We were seeing the continuing birth of the Big Island. Eventually the fires here will die, but a new island will emerge off to the south (it's already got a name: Lo'ihi. Look for it to appear in a few thousand years).
It's not entirely true to say that we never saw Pu'u O'o on the trip a few weeks ago. There is a spot on Highway 11 near Glenwood Road and the Hirano Store where the cone can be seen. During our reconnaissance before the students arrived, we stopped and had a brief look (below). Of course, once the students were with us we tried again, but it was hidden in the rain.
The Pu'u O'o as of this writing has advanced three miles down the upper slopes of the east rift zone and is approaching the coastal pali. If the eruption keeps up, the flow may once again reach the sea, and once again cover the extension of Chain of Craters Road. After the close call of 2014, the road was rebuilt as an emergency escape route for people in the Puna District. Such are the risks of living on an active volcano.

In the next post, we'll see evidence of a conflict between the gods and humans as they settled the island, a conflict that continues today.