If by chance you are wondering why it's such a hazard to operate commercial aircraft is these conditions, the first is erosion of the cockpit windows, to where it is difficult to see out of them .
Second, is the volcanic ash has a high silica content, when the ash gets into the 'hot' section, or combustion area of the engine, the silica melts, and then a deposit of 'glass' gets on the parts and destroys the efficiency of the engine .
All of the rotating parts downstream of the combustion area, are airfoil shaped , and any deposits on them greatly reduce their capability to do their job .
Worst case scenario, the engine quits running, and in most cases, can't be re-started .
After a turbine engine ingests volcanic ash, it needs to be completely torn down, and all parts with a glass coating, must be replaced .