Ash cloud diagram (IMAGE) University of South Florida Caption Numerical model allows scientists to reconstruct eruption rates through time by estimating the dimensions of the umbrella clouds that contribute to the accumulation of vast deposits of volcanic ash. Credit University of South Florida Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.