Imagine that you are Gunung Merapi and that nobody cares about you since there is much more famous volcano named Gunung Merapi. And to make things worse it is also located in Java, Indonesia. So, you think long and hard and through a few well placed eruptions you create a side vent with a very special feature. And once more you are neglected since everybody knows your nice new side-vent and forget about you even more.
Kawah Ijen is located inside the Kendeng Caldera (sometimes called Ijen Caldera). Kendeng has no less than 4 ring-fault volcanoes that are known as Ringgih, Merapi, Ranteh and Jampit. There are two extra caldera volcanoes, Suket and Raung and to top it off there are 13 intra-caldera volcanoes and vents. One of those intra-caldera vents is the side vent of Merapi that we are going to talk about today.
It is the spectacularly well known Kawah Ijen, most famous for its blue flames burning in the night and the sulphur mining that is being done there. The last part is probably the most dangerous line of work on the planet.
It is though the least well known feature that we are going to talk about today. Inside the crater is a 1000 by 700 meters baby blue lake. Normally amateur poets would descend on such a lake to write bad poetry, but in this instance that will not happen since we are talking about one of the world’s largest potential natural disasters.
Anyone who has ever gotten a drop of car battery acid on their hands knows how acidic that is. A car battery has a ph around 1. Kawah Ijen has 0.2 in ph, and it contains 31.5 million cubic meters of acidic brine caused by sulphuric gases being scrubbed in the rain-water filled lake.
So, basically what looks like water is sulphuric acid that is diluted by salt water and particulate matter that is suspended in the mix. In this case 1 liter of water contains a whopping 100 grams of particulate matter. The amount of sulphur is so high in the water that large rafts of sulphur float on top of the water. And to compound the problem even further, the water is high in heavy metal content.
The lake is kept intact by a natural dam that has been reinforced due to structural weakness. But, to all points and purposes even a small volcanic event, an ill placed earthquake, or even natural erosion, is all that stands between the nightmare waters of Kawah Ijen and a city of 1.2 million people. And then we have not talked about the effects on the river system that irrigates countless farms in the region. To all points and purposes it would be the largest industrial accident in history, only that it would be nature itself that stands for the devastation.
This has made the Indonesian Government to make a broad call for ideas upon how to actively mitigate the hazard of Kawah Ijen.
Risk of Active Mitigation of Lake Ijen
As late as 2012 there was a high degree of unrest in the volcano caused by an intrusion of magma at very shallow depth, probably the intrusion was as shallow as 1.8 kilometers below the volcano. This directly affected the water table below; in turn this caused blasts of acidic water, sub-aquatic emission increase and increased temperature of the lake.
With such a shallow intrusion of magma any lowering of the over-burden pressure causes high risk for an eruption. As such, fast removal of the water would most likely cause the catastrophe you are trying to mitigate.
An outline for active mitigation of Kawah Ijen
As I see it there are 3 ways that you could mitigate the hazard. I will begin with what I perceive as the worst way to try and go about it. And that would be to try and scrub the acidity in situ.
The simplest way would be to use helicopters dropping finely ground calcium hydroxide (slaked lime) into the lake, or pumping a slake lime solution into the lake. This would raise the ph of the lake and increase particulate size sufficiently to remove a lot of particulate matter since gravity would force it down towards the bottom of the lake.
The problem is that this would involve such large volumes of calcium hydroxide that you would quickly raise the level of the lake so that you risk compromising the precarious dam. You also risk clogging up the hydrothermal vent systems in the lake so that pressure rapidly increases and a series of hydrothermal detonations causes an eruption.
In my view this would at best produce a less acidic outburst of water and at worst it would cause the dam to burst before you have gained any effect at all.
Solar powered mitigation
In this case you would drill a wide bore non-corrosive tube at an upwards angle into the lake so that the opening is at about 100 meters depth. This would ideally in the end remove 80 percent of the available water over time and greatly reduce the risk of dam failure, or that an earthquake would pierce the crater wall in such a way that water came out. It would also severely decrease the risk of a spill out during an eruption.
If this is done over a prolonged time the risk for a de-pressurization eruption is fairly low, and even if it happened there would inevitably be less water contained in the lake. And in this case every single meter the lake is lowered is a victory. Because, whatever we do the volcano will sooner or later erupt again.
If you increase the rate of removal with ten liters of water per second you would empty out the lake completely in 100 years time. If you aim at removing 80 percent of the water it would take 80 years at this speed. Just remember that every single meter of lowered water level in the lake would be saving lives.
Removing all of the water is in this case pointless, the point is to make the problem manageable and diminish the risk of dam breaching and earthquake spill over. There is also a high risk for local tsunamis caused by crater wall landslides and seiches.
The idea here is that you build a series of meter deep square ponds out of concrete, perhaps 10 by 40 meters and cover them with black roofs. The black roofs would create a warm environment that would increase the rate of H2O loss and in a little while you would get a powdery residue of sulphur, salts and metals.
After enough refills you get a deep layer of residue that you would need to remove. Here you would need to employ quite a bit of cunning since we are talking about highly toxic waste. You would need to find a cheap way of removing the sulphur and sell it to local sugar factories, the metallic salts could be sold for its metal content if you are lucky.
The worst case scenario would obviously be to dig all of it down and cover it up while you wait for the next big eruption.
The advantage is that it would be fairly cheap and create a few jobs locally. But, the problem is that it would be creating a lot of highly hazardous waste, about a kilogram per second if you would be handling the minimum of 10 liters of water per second.
Water treatment mitigation
This is my preferred option. The greatest drawback is that it would cost more than the solar powered version and about the same as the calcium hydroxide injection into the lake. But it would produce dramatically less toxic waste (but the same amount of waste) as the solar powered solution and be far safer than either of the other solutions. It would also create a few local jobs.
It begins with the same wide bore pipe being drilled in as with the solar powered solution. But instead of being dried out by heat you treat it as waste water.
The first step would be treatment with calcium hydroxide to raise the ph-level to the ambient level of the river you will in the end let the water out into. The calcium hydroxide will create larger particles that can be scrubbed out of the water.
Next step is repeated aeration of the water to make the particulate matter buoyant, this makes it easier to sweep it out since it would create foam on top of the water.
The next step is sand filtration passages to remove the last of the particulate matter. By now any particles would either be at the bottom of pools ready to be sucked up and dried, or scrubbed away as foam and dried, or being stuck in the sand filters.
The reason for removing the particulate matter is that it would as the water is released end up in the gills of any fish in the river systems and risk killing them over time.
By now you have ph-neutral water that is low in particulate matter and with a manageable content of heavy metals. Some heavy metals still remain in the form of salts, but there is little you can do about it without incurring massive cost. And remember that these metallic salts would anyway unceremoniously be dumped into the river systems if the dam breached or there was an eruption at Kawah Ijen in far greater amount than from the treated water.
The remaining water would then be allowed to flow down into a river dilution pond where it is diluted with a factor of 1 liter per 100 liters of fresh water before being injected into the river system. Since the water is slowly let out and is far less toxic it would not constitute a health hazard for the population, nor would it endanger the flora and fauna.
The waste would mainly be constituted by various sulphates, carbonatites and silicates. These are fairly inert compared to what the volcano already contains, so they could safely be reinserted into the volcano. This would as it happens lower the de-pressurization with 10 to 20 percent. As such it could help to delay any de-pressurization eruptions from happening, and it would for all points and purposes be a pretty good place to store it in since the volcano either way would have ejected it in a far worse form if it had been left alone.
Active Mitigation of a volcano is at best controversial. At Kelud the lake has been mitigated for a long time, a practice that has saved a lot of lives during the last eruptions. At Kawah Ijen the risks are far greater since the mitigation might produce a premature eruption. But, in the end you are risking to set off prematurely what would have happened anyway. And in the end, even just a few meters of less water height would shore up the dam and produce a significantly diminished acidic lahar.
To me the benefits would be larger than the risks. Here I leave it to the respected readers of Volcanocafé to do what they do best, discuss matters and weigh in. I think that anyone who is really going to do this project could do worse than read the comment field.