Living with Volcanic Ash: Lessons for Auckland from Kagoshima City, Japan

Today, I warmly welcome another guest post from Daniel Blake, Doctoral researcher at the University of Canterbury.

 Daniel had the opportunity to visit Kagoshima City in Japan recently and learn about how the city residents and authorities deal with the frequent volcanic ashfall from one of my favourite volcanoes: Sakurajima. His PhD focuses on the impact of ash on roads and vehicles – the main focus of this post is on that topic, following discussions he had with Kagoshima City Office staff and road cleaning contractors, and observations from the field.

Go for it, Daniel!


Kagoshima is one of the most southern cities in Japan, with a population of over 680,000 people, around half the number who live in Auckland City. Just 4 km across the harbour lays Sakurajima, an active conical volcano, which dominates the skyline to the east of the city… at least on a clear day!

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A small eruption at Sakurajima Volcano into the cloud (taken from Kagoshima City on 09 June 2015).

To help put things into perspective, Sakurajima Volcano covers about three times the area of Rangitoto Island and is about four times its height. Although there are differences between the processes that formed Sakurajima and the volcanoes in the Auckland Volcanic Field, we can learn a lot from how Kagoshima City residents, council staff and contractors manage and live with volcanic ash. The most recent activity started in 1955, and at the time of my visit (early June 2015), there had been over 630 eruptions since January!

Impacts on roads

When speaking to the Kagoshima City Office staff, some of the key challenges that residents face when driving on ash-covered roads became clear:

  1. They suggested that just 1 mm of volcanic ash deposits are enough to make road surfaces slippery.
  2. It was also implied that ash of more recent eruptions (from the Showa crater of Sakurajima) appears to be less slippery than that of older eruptions (from the Minami-daki crater), probably due to the smaller particle size associated with these recent eruptions.

… Bingo! Both of these findings aligned perfectly with recent road surface traction testing I was conducting in the lab back at the University of Canterbury so I was very happy to hear them!

Interestingly, the officials said that it was very difficult to drive when ash depths exceeded 1-2 cm and that most roads would be closed to vehicles for any depths greater than 2 cm. These depths were slightly less than I had expected after studying research from other eruptions. There is often an increase in accident rate during ashfall, particularly on roads around Sakurajima volcano itself, perhaps because the ash particles are coarser nearer to the volcano and the road surfaces become more slippery, but perhaps because the roads are windier too.

Another impact that drivers in the city often face is the reduction in visibility from ash particles suspended in the air, sometimes to just 20 meters or so. Apparently, low visibility can be worse during ash that has remobilised from the ground (when vehicles drive over ash and stir it up) than from the initial ash fall from the eruption. Although lower speed limits are not implemented in ashy conditions, drivers usually slow down as a precaution and turn on their headlights.

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Vehicles driving in low visibility caused by volcanic ash in Kagoshima City (photo courtesy of Kagoshima City Office).

The importance of road markings should not be underestimated! This was highlighted as one of the important issues in the city as only small amounts of ash falling on roads is enough to cause markings to be hidden. When road markings are obscured, it becomes more difficult to drive, especially to stay in the correct place on the road or to see pedestrian crossings. This has the effect of reducing road safety. Additionally, the officials at Kagoshima City Office also use the coverage of road markings as a prompt to start cleaning up volcanic ash from the roads.

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Road markings become hidden by very small amounts of ash, making it difficult to drive and reducing road safety (photo courtesy of Kagoshima City Office).

Ash removal

Wow! What a mission ash removal from roads in the city is…

One of the main goals is to clean most of the ash from all roads within 3 days of any eruption. This requires extensive planning and 97 ash road sweepers can be quickly mobilised across the Kagoshima and Sakurajima area. However, this is often not enough sweepers to cope with larger eruptions when some need to be sourced from other areas in Japan. During an eruption, the staff at the City Office monitor CCTV cameras and other information from the press, TV and social media to determine when and where to send field officers and to determine which parts of the city need to be cleaned.

The city is divided into 92 blocks for cleaning purposes and different contractors may be responsible for cleaning different blocks. Specially adapted road sweepers are used for the clean-up which are capable of clearing ash up to 2 cm thick. They have greater suction and the brushes rotate faster than typical road sweepers. A rubber flexible barrier attached to the front in the centre prevents ash blowing up and away from the vehicle.

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Specially adapted road sweeper in a Kagoshima City contractor depot.

The specially adapted road sweepers also have extra water spray pipes fitted. Indeed, huge amounts of water are used during cleaning as a sprinkler vehicle also follows each road sweeper to wash a lot of the remaining ash away (a little always remains though). Each of these vehicles alone may use up to 6.5 tonnes of water in just one hour!

The Kagoshima City Office calculated that 1,274 cubic meters of ash was cleared from the city roads in 2014, and 2014 wasn’t an especially busy year!

Ash doesn’t just accumulate on the city’s roads… it gets everywhere… on roofs, vehicles, in gardens and even within houses. In fact around 8,200 cubic meters of ash was removed from residential areas by Kagoshima City Office contractors in 2014. It is collected from over 6,500 designated ash collection sites across the city, each marked with a sign to show that residents can leave bags of ash there for collection.

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One of the 6,500 or so ash collection sites across Kagoshima City and on Sakurajima.

Kagoshima City is certainly well set-up to manage ash fall and has heaps of experience. Imagine the challenges that we could encounter in Auckland, especially when driving and having to remove ash from our city’s roads and residential areas!

[Editor’s note: Wow, these pictures and information really illustrate what a nuisance ash can be to drivers. I can’t imagine trying to drive in Auckland under those conditions! Unfortunately, of any volcanic hazard, Auckland is most likely to experience ash fall–this is because distant volcanoes like Ruapehu can send ash our way if the wind is blowing toward us. It’s a good thing we have people like Daniel studying how ash would affect Auckland roads, and all the ways that other people deal with ash!]

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