Kaimondake volcano is a picturesque stratovolcano at the southernmost tip of the main Japanese islands. As a volcano, Kaimon-Dake is almost too perfect. Its shape is almost comically conical, where it rises out of the ocean to greet sailors navigating into and out of the Kagoshima Bay. Beyond this, you can even hike to the top of the volcano and see the beauty of the surrounding landscape and ocean.
If you were teaching a 3rd grade student what a volcano was, Kaimon-Dake would make a great example with the exception of one important part: recent eruptions.
The point here is, Kaimon-Dake looks like a very typical stratovolcano, and in some ways it is. But there is also a lot more complexity here, and some very good reasons people should get to know Kaimon-Dake and the surrounding volcanoes of the Ibusuki Volcanic Field.
A Brief Overview of Kaimondake and the Ibusuki Volcanic Field
Kaimondake is not particularly old. In fact, it is one of the younger stratovolcanoes in the world with an age no older than 4400 years since its birth. This is evident by its somewhat modest size of rising only 924 meters above the nearby ocean. The lack of age also is evident through the fact that there is not many erosional patterns on its slopes along with the steep angle of the cone. Despite its young age, Kaimondake already has a composite edifice made of basalts with a sizable andesite lava dome perched on its summit.
While Kaimondake may seem like a brand new volcano, in many ways, it’s just an older part of a bigger volcanic system. The region that Kaimon-Dake sits in is a part of a highly-active volcanic region: the Kagoshima Graben (read more about this in my post on these volcanic systems), and it is typically associated with the 15 x 25 km Ata caldera which is the the source of major pyroclastic flows during its formation more than 40,000 years ago.
In that sense, Kaimondake is sort of a Somma Volcano on a caldera rim, although it may lie slightly outside the boundary of the Ata caldera system (which there is conflicting information regarding its precise location anyway).
This entire region near the Ata caldera has been extremely active through the holocene… until recently. Beyond Kaimondake, there are numerous large maars that are the sources of pyroclastic surges, and quite a few smaller nested calderas, including the picturesque Ikeda Caldera, which formed during a large phreatomagmatic eruption not long before Kaimondake was born just a little bit to the south.
Stating it bluntly, if another episode of one of these phreatic or phreatomagmatic events were to occur, it would be really bad news. You would likely see a very sudden pyroclastic surge that would devastate the nearby regions. Luckily, they do not happen that often, although they happen frequently enough on a geological time scale that concern and monitoring should be required.
The Strange Eruptive History of Kaimondake
Most volcanoes have a tendency to be somewhat periodic. They don’t follow easy to read patterns, and many volcanoes erupt too infrequently to be confident in any predictions based on volcanic patterns.
With that said, there are a few volcanoes in the world such as Katla that have gotten much closer to being somewhat predictable in a very broad sense. For a while, Kaimondake could have been seen as one of these volcanoes.
From the time of its birth until around 885 AD, Kaimondake erupted over 25 times and formed the entirety of its edifice. The majority of these eruptions were vei 3-4 size, similar to what we have seen at Katla. See below for the eruptive history with repose period added.
|Date||Eruption Size: VEI Scale||Repose Time|
As one can see, there is not much of a repose period here until the recent period.
The longest repose in its short history was 750 years, and the majority of the eruptions came within short 50-100 year spurts of activity. Considering that many of these eruptions were decent sized VEI-4 eruptions (some may have been larger), this is extremely impressive output considering how young the volcano is.
What makes this slightly strange is the fact that most young stratovolcanoes need to build a magma chamber before they start emitting larger eruptions. In the case of Kaimondake, the larger sized eruptions started right off the bat, and continued until it became silent. It also has already switched from being basaltic in nature to having andesitic lava-doming activity. These are all signs of more evolved volcanic activity, which can possibly be related to kaimondake being inside a large volcanic field.
Why Did Eruptions Stop at Kaimondake?
This is the important question and what many people are likely wondering. For such an active and young volcano, why did eruptive activity suddenly stop after being so regular? As we mentioned before, the longest repose period 750 years between eruptions (from 1450 BC to 750 BC).
Was there ever a pattern to begin with?
Part of the issue is that people like to see patterns, it’s human nature. For Kaimondake, there may have never been a pattern of output to begin with. For a volcano, the lifespan of less than 4400 years is extremely young to form the basis of any patterning on, so we can’t really say that Kaimondake is actually breaking its eruptive pattern since we don’t really know what those patterns were like in the first place.
For a volcano such as this, we could assume a few potential scenarios.
- Activity has stopped or temporarily decreased because magma stopped being supplied to the primary magma chamber. This would fall within the normal expectations that volcanoes receive magma from depth periodically, and not in a constant manner.
- Magma from depth has chosen a different path, and is no longer being supplied to Kaimondake. Knowing the region, this is very possible considering that magma is maybe now being pushed into other regions such as that of lake Ikeda.
- Magma is still arriving at Kaimondake, but the lid is a lot stronger this time around, or the rate of magma accumulation is simply slower. This could be a scenario of future concern, although there are no current signs of unrest.
The main takeaway here, is that just because a volcano changes its perceived pattern doesn’t mean there is cause for concern, and it doesn’t necessarily mean that a new large eruption is looming. As I like to say, things are subject to change, so while patterns can potentially be used as a reference, they are not to be used for predictive purposes.
With that said, there can be at least some potential for a larger eruption with a longer repose time, but things aren’t that straightforward. If Kaimondake were to wake up again, it would be a volcano that would concern Japanese Authorities due to the history and style of its eruptions as well as the eruptive activity of nearby volcanoes in the Ata Caldera system.
Inflationary Studies of Kaimondake?
One final thing that I would be curious to know that I don’t have the answer to is whether there is any notable uplift along the shores of Kaimondake. Since it is a shoreline volcano, we should be able to figure out uplift of the edifice if the proper techniques are tested (Albert at Volcanocafe knows a thing or two on this).
If we were to know the inflation here, we could learn a lot more about whether Kaimondake is priming itself for a bigger eruption, or if it simply has slowed down from its explosive initial growth.