One of the more difficult to visit volcanoes in the world sits on the border of China and North Korea. It was the source of a VEI 7 eruption in the vicinity of 969 AD which ejected over 150 km3 of debris, creating a caldera some 5 km in diameter. That caldera is now filled with a crater lake called Heaven Lake. The mountain stands some 2,744 m tall, making it one of the tallest mountains in that part of Asia.
It is revered as the ancestral home of the Korean and Manchu peoples.
The mountain is known by various names mostly due to the number of different languages spoken in its vicinity. From the Wiki (which in some things works far better than others), it is known as Changbaishan (Perpetually White Mountain) by the Chinese. It is also known as the Tianchi volcano by the Chinese. The mountain and lake together are known as Baitoushan (Whitehead Mountain) in Chinese. This name has been modified as Paektusan (or Paektu-san) in North Korea and Baekdusan (or Baekdu-san) in South Korea. There are also more obscure variations of the name in Manchu and Mongolian both of which mean White or Lofty White Mountain. This along with various translations of the name from the four or five Oriental languages involved to English, German or whatever else make research interesting.
That part of Asia has vibrant civilizations for many thousands of years, so a large, active stratovolcano capable of ejecting 150 km3 in a single eruption is something those civilizations will tend to pay close attention to. And so they have.
The mountain was first documented in a compilation of Chinese mythic geography in the 4th Century. The current Chinese name was first used around the time it had its large eruption (+/- a century or so).
The Koreans have long viewed it as their ancestral home. Kim Il Sung claimed he was born there in an attempt to appropriate the spirituality of the mountain for himself and his new nation. He also claimed to organize his armed resistance against the Japanese there.
South Korean access to the mountain takes place from the Chinese side.
As to be expected, when three nations hold a mountain on the border as sacred, ancestral home to their people there have been a variety of border disputes and treaties over the years.
What does it take to build a large stratovolcano capable of this sort of eruption? One would normally immediately point to subduction. The problem is that Baitoushan (Tianchi) is located over a thousand kilometers from the nearest subduction zone in Japan. But subduction may still be in play, though not in the way that most of us may think.
It appears that the Pacific Plate impacted the Asian Plate at a relatively high speed and the subducted plate is still present under the region as a very deep, but observable chunk of flat palate. At its observed depth of some 500 – 600 km and length of time it has been there, it should be mostly dehydrated with little moisture left.
There is a region of upwelling mantle above the dehydrating, stagnant Pacific Plate slab underlying the region. A line of very deep earthquakes sit to the east of the volcano. These earthquakes are some 500- 600 km deep. This mantle upwelling drives a continental rift system that allows the melt to reach the surface. This is referred to as the Northeast China upwelling.
So in some ways, this is purely intraplate volcanism. Yet in others we have our old friend, flat plate subduction perhaps in play.
These volcanoes behave very much like intraplate volcanoes rather than subduction volcanoes, though some subduction may be in play.
The basic unit for Baitoushan (Tianchi) appears to have started prior to 28.4 MY ago with the formation of a basalt plateau. This strongest series of eruptions formed at least five shield volcanoes to the north and southwest of Baitoushan (Tianchi) between 21.6 – 10.4 MY ago.
The next series of plateau forming eruptions took place between 5.6 – 2.5 MY ago. While these were primarily basaltic in nature, at least two of the volcanoes involved show what the author describes at:
“…direct evidence of magma differentiation. The eruptions of trachyte and comendite magmas reflect a long period of differentiation from the parent basaltic magmas.”
Baitoushan (Tianchi) itself shows similar evolution. There were at least four eruptive periods of activity ranging back at least 20 MY ago during the basalt plateau formation eruptions. This was followed by at least three basaltic shield volcano formation eruptions between 4.2 – 0.1 MY ago. The trachyte cone building eruptions demonstrating increasingly evolved basaltic magmas started some 2.1 MY ago. The most recent phase is characterized by highly evolved rhyolitic – trachyte eruptions. There are also parasitic cones on its flanks oriented much the same direction as the underlying fault line.
The change in eruptive style has been suggested as a result of tectonic uplift over the last 3 MY in the area of the Korean Peninsula, Sea of Japan and the Changbai Mountains, with one paper suggesting thickening of the crust under the area. http://www.sciencedirect.com/science/article/pii/S0024493706002982
Recent activity of the volcano was suspected in 2010 and 1994. Both included reports of gas emissions, hot springs and volcanic tremors. Chinese volcanologists dispute the 2010 report.
There was a rather significant earthquake swarm under the volcano that peaked in 2003 Larger earthquakes during the swarm peaked in 2004. Earthquakes during the swarm were more than 100/day. Two years later, the swarm had dwindled back down to background levels, under 12 a month.
The most recent eruption April 1903. It produced comendite – rhyolite pumice which was deposited on the eastern and southern slopes of the volcano.
The 969 AD eruption is thought to be one of the largest eruptions in the world over the last 10,000 years. It is thought to have proceeded in three phases, which emptied a magma chamber of well evolved magma. The eruption kicked off with a Plinian or super-Plinian plume. It deposited trachyte and rhyolitic pumice as far as Hokkaido, Japan some 1,200 km east. The second phase started when the plume collapsed and significant pyroclastic flows were produced. These flows extend as far as 70 km from the vent. Volcano Discovery believes there was a period of repose between the Plinian and the pyroclastic flow phases. Both phases are thought to have been very short, depositing some 95% of all eruptive materials in a period of a day or two.
The final phase was phreatomagmatic, after which most of the gas-rich highly evolved magma had been erupted. This phase produced less evolved magmas in the form of trachytic pumices. http://www.volcanodiscovery.com/changbaishan-eruptions.html#er737
Estimates of the total amount of ejecta range from 30 – 150 km3. I tend to believe the upper number is more accurate than the lower one.
There were another pair of VEI4 eruptions of Baitoushan in 180 BC and 2160 BC
One of the interesting things about the 969 AD eruption is that it does not correlate with significant climate change. At the time, the world was warming up from the climate crisis of 540 AD. While ice cores dated to the time of the eruption do show the expected ash spike, they do not show significant or extended global cooling.
Why this result? Probably the most important reason is that this eruption was relatively sulfur-poor. On the other hand, it was significantly ash rich, leading to the conclusion in at least one paper that chemical composition of the eruptive products is as or perhaps more important to the climatic impact as the sheer volume of ash injected into the atmosphere.
Another and perhaps related reason is pure speculation on my part follows: Perhaps the location of the volcano at a relatively high latitude was enough to keep the injection of ash and SO2 25 – 30 km into the Stratosphere spreading south into temperate zones and across the equator. In certain times of the year, particularly during the winter, the circumpolar jet stream is very strong and will tend to keep whatever is in it blowing east and west rather than north and south.
Baitoushan remains one of the more dangerous volcanoes in China. Any active volcano with occasional earthquake swarms and active hot springs and fumaroles is not going to go dormant any time soon. Due to the rather interesting national imperatives for the two nations sharing its flanks, it is not nearly as well monitored as it should be. This may be a problem some day.