Christopher Samuel Youd, commonly known as Chris Youd, was a notable British geologist and geomorphologist. He is best known for his work on the processes of soil erosion and sediment transport, contributing significantly to the understanding of landforms and landscape evolution. His research has had a lasting impact on the fields of geology and environmental science. Youd was particularly recognized for his studies on the phenomenon known as liquefaction, which occurs when saturated soil loses strength due to applied stress. His findings have been influential in assessing risks related to natural disasters, such as earthquakes, and have informed engineering practices in civil engineering and geotechnical engineering.