The phrase "a volume of ash" is correct and usable in written English.
It can be used when referring to a specific quantity or mass of ash, often in contexts related to geology, environmental science, or even cooking.
Example: "After the volcano erupted, the landscape was covered with a volume of ash that altered the local ecosystem."
Alternatives: "an amount of ash" or "a quantity of ash".
For example, the second phase of the 2010 eruptions of Eyjafjallajökull was classified as VEI 4 despite a modest 8 km high eruption column, but the eruption continued for a month, which allowed a large volume of ash to be ejected into the atmosphere.
Maeno et al. (2016) estimated a total volume of ash-fall and pyroclastic density current deposits of 0.7 1.3 × 106 m3.
"The soil in the area covered by this volume of ash deposits will be practically lost," said Wilfredo Vera, engineer from the University of Chile.
The volume of ash and issues with the clogging of air filters also meant that clean up vehicles struggled to gain access to some areas for clean-up.
Comparison of the ash-fall distribution between the 2014 and 1979 deposits in the proximal area, however, shows that a relatively larger amount of ash accumulated proximally during the 2014 eruption than during the 1979 eruption, even though the total volume of ash was less.
The volume of ash deposited, and the estimated height of the eruption plume (43 kilometers above sea level) put the eruption's magnitude at a minimum of 7 on the volcanic explosivity index (which has a scale of 1 to 8)—making it one of the largest known in the Holocene.
Because the eruptions are small, the volume of ash from each eruption is usually too small to estimate, but H. Shinohara (AIST; Advanced Industrial Science and Technology; personal communication, 2005) calculated an ash weight of 4 × 106 kg for one of the largest eruptions, which occurred on 2 December 2004.
"The volume of ash and water was nearly 100 times greater than the amount of oil spilled in the Exxon Valdez disaster".
The single isopach method (V = 12.2TA; T: thickness, A: selected isopach area; Hayakawa 1985) is sometimes used to estimate the volume of ash-fall deposit (and widely used in Japan), because the total discharged volume can be calculated based only on one isopach.
