Guy Carpenter has built a fully probabilistic ash-fall model for six volcanoes in Japan.

It says eruptions from Fuji, Hakone, Asama, Haruna, Kita-Yatsugatake or Kusatsu-Shirane could affect the highly populated and industrialised prefectures of Tokyo and Kanagawa.

The model estimates damage to residential, commercial and industrial buildings from vertical ash loads.

Guy Carpenter Catastrophe Risk Analyst Delioma Oramas-Dorta cites the model in an article for BRINK – parent company Marsh & McLennan’s digital news service.

More than half of the 20 cities most at risk from volcanic eruptions are in the Asia-Pacific region, she says, referring to the Lloyd’s City Risk Index.

The threat remains poorly understood. A repeat of the 1707 Mount Fuji eruption could cost the Japanese economy more than $US22 billion ($30 billion) – without factoring in effects on aviation, utilities infrastructure and other vital industrial assets.

“Just because large and very large eruptions have not occurred in densely populated areas in the recent past, we cannot ignore the catastrophic impacts such events could have now,” Ms Oramas-Dorta said.

“Fine ash fall that infiltrates into buildings can cause damage to sensitive equipment, potentially leading to widespread interruption of business and services.

“Removal and clean-up of deposited ash can lead to rapidly rising costs, particularly in cases where eruptions last weeks and months.”