Those planning on landing in Alaska need to take account of the ash stratification at different altitudes based on wind differences at those altitudes.
By this time the company dispatch and routing procedures should know what routes and altitudes are at risk and advise their flights.
If you don't know than don't go.
If you get caught by surprise (St elmo's fire, acrid smell, etc.) then don't advance the throttles.
By now every cockpit should have SOPs to cover this