Since it resumed activity in 1955, the volcano has been erupting almost constantly ever since. Thousands of small explosions occur each year, throwing ash to heights of up to a few kilometres above the mountain. The current forms of explosions consist of spouting rocks, ash and gas from a crater on the top of the Minamidake peak (1040m). It generates 10 to 30 million tons of ash each year. Ash from the volcano falls on the city up to 143 days a year and 100mm in annual depth.
Monitoring and predicting large eruptions of the volcano are particularly important because of its location in a densely populated area, with Kagoshima's 600 000 people just a few kilometres from the volcano. The city conducts regular evacuation drills, and a number of shelters have been built where people can take refuge from falling volcanic debris.
There is serious agronomic damage caused by the ash, particularly when ash falls at critical points in the growing season. Pumice ash can also kill fish in fish farms. The discharge of volcanic gases such as sulphur dioxide is a significant issue as the gas can travel hundreds of kilometres and not only produce acid rain, but also can cause death in extreme situations.
The impact on human health is not as significant as it is thought out to be. People still go to work when ash falls, using umbrellas to shield them from the ash. Although no medical proof yet exists, it has been reported that susceptible people experience respiratory illnesses when exposed to the ash, and that neonatal death rates may be affected by volcanic sulphur dioxide concentrations in the city.
Measures in place
An array of mitigation measures is in place in the city, including a 220-million-Yen-per-year operation to keep the city streets clear of ash. Residents are expected to collect ash from their properties in yellow supermarket type bags and put it out at one of 5504 collection sites twice a week. Hand sweepers are used to sweep pavements and around houses. Public workers in this occupation wear eye protection, basic facemasks and helmets (to prevent ash from getting into the worker's hair).The most pertinent problem for the city is that ash falls on the roads and obscures the road markings, causing traffic problems. It is also slippery when wet. The city has a target to sweep up the ash within