According to Tokyo University, recently, ash from Nishinoshima Volcano has become complete different compare with its ash before.
Ash from Nishinoshima was more like rocks before. But now, ash becomes more like similar one in Kilauea in Hawaii. Ash becomes more like soft sand rather than hard rocks.
This proves Nishinoshima is getting higher temperature magma from deeper magma chamber.
When Nishinoshima is getting magma from deeper magma chamber, the number of explosive eruption has started increasing.
If these kind of eruption continue for a year, Nishinoshima will be 700 meter high. Right now, Nishinoshima is 200~300 meter high.