降灰

1. Origins, structure, and basic meaning

• Structure: 降灰 is read as こうはい and is a noun for volcanic ash falling from the air and settling on the ground, buildings, or surrounding area.
• Basic usage: Evidence of a past ashfall appears in 過去の降灰, while the sky turning gray because of falling ash appears in 降灰で空が灰色になる.

2. Common pitfalls and similar expressions

• Ash falling and settling
  • It focuses on ash traveling through the air and settling over an area rather than on the moment the volcano produces it.
• Difference from 噴火
  • Unlike the term for the volcanic eruption as a whole, this word specifically identifies the resulting fall of ash.