Mount Chiginagak sits some 600 km southwest of Anchorage, roughly situated on the Alaska Peninsula between Aniakchak and the Katmai Volcanic Complex. It is a single peak that tops out at just over 2,200 M. The peak itself is composed primarily of andesitic and pyroclastic layers. It also has basalt lava flows with some evidence of recent pyroclastic flows. It has several dacitic domes on its flanks which have collapsed from time to time in the past. The mountain itself is glacier covered at its peak with a small crater some half a km in diameter. There are active fumaroles on its flanks. Due to its relative inactivity and remoteness, the mountain is not monitored by the Alaska Volcano Observatory. http://www.avo.alaska.edu/volcanoes/volcinfo.php?volcname=Chiginagak
There are only a few recorded eruptions over the last 160 years, 1852, 1929 and 1971. The 1852 event was reports of smoke from the summit. The 1929 event is classed as a questionable eruption, primarily due to the inability to differentiate between what was happening on Chiginagak and neighboring volcanoes. The 1971 event was a small ash eruption observed from Port Heiden that lasted less than a single day. http://www.avo.alaska.edu/volcanoes/activity.php?volcname=Chiginagak&eruptionid=181&page=basic
In 1998, there were reports of snow melting and increased sulfur smells from the volcano along with more vigorous fumarole activity. There were reports of small clouds of black smoke and greenish yellow gas rising from two sources to 300 M or so above the mountain (likely with a strong sulfur dioxide / sulfuric acid content), and at least one morning a dark dusting of snow at the top of the mountain. http://www.avo.alaska.edu/volcanoes/activity.php?volcname=Chiginagak&eruptionid=182&page=basic
The most recent Chiginagak activity took place in 2004 – 2005. Increased heat flow into the vicinity of the crater melted snow and ice between November and May, creating a crater lake measuring some 400 M across and an estimated depth of 150 M. Somewhere in early May 2005, there was a catastrophic release of the fluid in the lake, creating a highly acidic lahar and water discharge traveling some 27 km downstream, flowing into and acidifying Mother Goose Lake along with the headwaters of King Salmon River which flows into Bristol Bay near Ugashik and Pilot Point. The lahar was accompanied by highly acidic aerosol cloud that killed surrounding foliage as high as 70 M above the water level of the creeks it traveled down. http://adsabs.harvard.edu/abs/2005AGUFM.V21E0675S
Aerial surveys found a breach through the crater wall that allowed crater lake waters to continue to flow downstream for nearly four years afterwards. At the end of that time, fumarolic activity in the crater had decreased to the point where the lake started freezing over during the winter. Along with this, the lake level dropped to the point where it no longer was able to flow out of the breach.
Water out of the lake had significant sulfuric acid content, with high levels of dissolved metals and clays. It had sufficient volume to inundate a lake, acidify the entire water column to a depth of 45 M to a pH of 2.9, destroying a salmon run and spawning habitat in the lake (red salmon usually spawn in lakes). Between 2005 – 2011, the pH of the lake returned to the normal range of 6.9 measured in September 2011.
Volcano and Indecision Creeks which feed into Mother Goose Lake were supplied with crater lake water for some years after the breach, and have been slow to return to normal pH levels. Indecision only made it back to a pH in the vicinity of 4 in August 2010. Researchers believe the crater lake continues to drain under a glacier on the south side of the cone, with that water feeding into Indecision Creek and finally into Mother Goose Lake. They also believe that similar crater lake breaches have happened in the recent past as there is anecdotal evidence from aerial photography and local lodges that something similar took place in the mid-1970s and early 1950s. http://www.dggs.alaska.gov/pubs/id/25602
As the water in the lake returns to normal, the salmon have started to return to the King Salmon River and Mother Goose Lake.
Carl wrote about this in November, 2013 as part of a column asking Volcano or Environmental Disaster? https://volcanocafe.wordpress.com/2013/11/18/volcano-or-environmental-disaster/
There are lots of ways for a volcano, even a relatively inactive volcano, to surprise us. And this one certainly did. There is a massive mine in the early stages of planning for the upper reaches of Bristol Bay. The anti-mining groups are fighting it via a variety of arguments, most of which boil down to lurid tales warning against an earthquake caused collapse of a tailings dam, and subsequent dumping of acidic water with dissolved metals into the salmon spawning grounds, destroying them and local fishing for all time.
Interesting that very thing just happened downstream of Chiginagak in 2005, a completely natural event, and the fish outside that particular watershed were not impacted at all. One lake and stream were damaged for a period of years, but the rest of Bristol Bay seems to be doing well.
And here again, the Friday riddles. The bar is open!
1. Bane of the Rattlesnake; It’s on the wrong track! (Clue: “I’d bring up Trafalgar, but that would be nauti!”) Answer: Trinidade (and Martim Vaz) in the Southern Atlantic Ocean, discovered by Estêvão da Gama aboard HMS Rattlesnake, dinojura44, 1 point.
2. In a field of one-hit-wonders, I stand alone. (Clue: You could have seen the last eruption at sunset. Final clue: It sounds like it’s in California, but it’s not!) Answer: San Francisco Mountain in the San Francisco volcanic field, Arizona. “San Francisco” was a one-hit wonder by Scott McKenzie in 1967 and the mountain stands out amongst many monogenetic volcanic cones. Sissel, 1 point.
3. Special sheep and loony toons? (Clue: The sheep are barbarians!) Answer: Tarso Toon in the Tibesti mountains. The Barbary sheep (Ammotragus lervia) are native to rocky mountains in North Africa, Kelda, 1 point.
|6 Shérine France
2 Evan Chugg
|1 Diana Barnes