Mount Ruapehu Crater Lake and the Coming Lahar of Hot Acid - 2.7.07 (part 1)
That's February second, not July second. I refuse to give in! Apologies for the quality of these photos...I was toting a point-and-shoot.
This past Wednesday I had the honor and privilege to help scientists from the NZ Institute of Geologic and Nuclear Sciences (where I work) and the Department of Conservation to the summit crater of Ruapehu volcano. Ruapehu, as many of you know, is home to three ski areas, two of which are large and full of some fun terrain when they have snow. Whakapapa and Turoa are two of my favorite places to ski in Aotearoa.
http://www.discoverourearth.org/stud...mt_ruapehu.gif
As some of you may also be aware, there is an acidic crater lake at the summit of Ruapehu.
Aerial over view of the volcano's crater in winter:
http://www.grantkaye.com/images/ruapehu/lahar.jpg
The lake holds almost several million cubic meters of water, which is about the same as the volume of the Westpac Trust stadium in Wellington.
http://www.holmesgroup.com/clients/Stadiumwgtnlarge.jpg
The water is heated to a comfortable ~27 degrees C (~78 F), and can have a nice Ph of less than 1. To add to it's beauty, there's slicks of liquid sulfur floating on the surface.
http://www.grantkaye.com/images/ruapehu/IMGP0052.jpg
My foot for scale, standing on wave-deposited sulfur on the shoreline
http://www.grantkaye.com/images/ruapehu/IMGP0053.jpg
The lake fills the bottom of the crater, but at the moment actually lies above the hard-rock rim and is held in place by a dam made of tephra (ash) and loose rubble that was erupted in 1995 and 1996, which is the last time Ruapehu was in action. So all of that hot, acidic, sulfurous water is sitting up there at 2500 meters, being held back by dirt and gravel. Not good. Every day, the lake level rises by around 1 or 2 centimeters. And every day, the water already seeping through the tephra dam eats away a little more at the front and the back.
http://www.grantkaye.com/images/ruapehu/craterlake2.gif
View of the tephra dam from January 2007:
http://www.grantkaye.com/images/ruap...rlakelarge.jpg
To make matters more tenuous, at the back of the lake an almost 200 meter tall serac of ice is eroding away steadily, calving huge chunks of ice into the lake. Every time a chuckn falls in, not only does it raise the water level when it melts, it sends seiche (tsunami in a lake) waves across the lake, and erodes the dam a bit more.
The ice wall at the other end of the lake from the tephra dam:
http://www.grantkaye.com/images/ruapehu/IMGP0023.jpg
A small seiche wave from a rather large and unsettling collapse while we were there:
http://www.grantkaye.com/images/ruapehu/IMGP0059.jpg
Add all this up, and there's a nasty situation brewing atop Ruapehu. A little more water, an earthquake, a huge piece of the glacier calving into he lake, or even a few days' hard rain, and the sucker is going to burst. Luckily, there's not too much in the way downstream, save for a few bridges, railroad tracks, and state highway 1. All of which have been fortified, along with plenty of warning equipment in place.
View of lahar debris from lahars during the 1995-96 eruptions (the 2007 one will come down the valley to the left of the one in this photo that is discolored)
http://www.grantkaye.com/images/ruapehu/ig-fig3.jpg
Map schematic of the lahar and the volcano:
http://www.grantkaye.com/images/ruapehu/ig-fig7.jpg
What's rad about being a grad student at GNS is that when they are short on personnel, the students get asked to help out. So this past Wednesday, I got the call - they needed an extra set of hands on Ruapehu the next day.
We drove up the night before, and crashed out at the GNS monitoring hut in Whakapapa village.
http://www.grantkaye.com/images/ruapehu/IMGP9968.jpg
The next morning, we awoke just before sunrise, and packed our gear up. Here's a shot looking out to the south.
http://www.grantkaye.com/images/ruapehu/IMGP9967.jpg
We drove around to Turoa, through Ohakune, the carrot capitol of the Southern Hemisphere, and made out way tot he lower parking lot at Turoa, where they are putting in another ski lift. Which is good for GNS, because there's a guy doing heli-pours of concrete for the lift tower foundations, so he is already up there (= less Hobbs minutes).
http://www.grantkaye.com/images/ruapehu/IMGP9970.jpg
Our ride for the day was a Squirrel (the kind with rotors, not the kind from Seattle with skins), which is a pretty powerful chopper.
http://www.grantkaye.com/images/ruapehu/IMGP9972.jpg
Funny thing - when I used to work at the USGS, when we'd fly to the lava flows on the Big Island, we had to do and entire days worth of training, and wear all kinds of special gear, and it was very official. Here, you get asked to go, and you get in the chopper. No special bullshit whatsoever.
We took off and hugged the ground up over the terrain of Turoa, and made it over the lip into the crater.
http://www.grantkaye.com/images/ruapehu/IMGP9976.jpg
http://www.grantkaye.com/images/ruapehu/IMGP9979.jpg
http://www.grantkaye.com/images/ruapehu/IMGP9982.jpg
The back serac wall of the lake from above:
http://www.grantkaye.com/images/ruapehu/IMGP9987.jpg
http://www.grantkaye.com/images/ruapehu/IMGP9988.jpg
http://www.grantkaye.com/images/ruapehu/IMGP9982.jpg
Pete the pilot dropped two of us off with all our gear, and went back for the others.
http://www.grantkaye.com/images/ruapehu/IMGP0017.jpg
Check out how eroded the dam is now:
http://www.grantkaye.com/images/ruapehu/IMGP0019.jpg
We landed (on the tephra dam), unloaded our gear, and had a look. Almost all the snow is gone from the crater, except for the perennial snowfields (one of which had turns on it!) and the top of the Mangatoetoenui glacier.
Turns:
http://www.grantkaye.com/images/ruapehu/IMGP0048.jpg
The tephra dam is eroding severely. Check out this photo taken at the beginning of January, in comparison to the one above taken a few weeks ago:
http://www.grantkaye.com/images/ruapehu/2monitoring.jpg
A few weeks ago, a GNS scientist kayaked out a lake-level
probe:
http://www.grantkaye.com/images/ruapehu/1kayak.jpg
Our goal for the day was to set up a $120,000USD laser scanner, and make a 3D map of the tephra dam. For the tech heads, it scans at a resolution of 200 mm over a distance of 350 meters. I'd like to see your Canon EOS 1-Ds do that Midget! GNS comes up here about once every two weeks to do this, to study how much of the dam erodes until it fails catastrophically and the lahar occurs.
The scary as shit thing here is that if it did go and we were standing on it, we'd have less than a minute to run off and onto high ground. Even worse is if the serac at the back of the lake fails, and a big enough chunk falls in to make a wave that erodes the dam - that would take about 30-45 seconds. The small waves we saw we timed at 35 seconds. About once every five minutes, you would hear a huge CRAAAACK just like a peal of thunder, and you would freeze while your stomach flipped upside down and you listened for the accompanying splash that meant "time to run for your life!"
