An Alluvial Fan in the Laboratory (IMAGE) University of Pennsylvania Caption Researchers used black sediment to represent large grains, or "gravel" in rivers, and white sediment as "sand" to create a model of an alluvial fan. Credit University of Pennsylvania 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.