Jan 13: “Sinking Cities”
Dr. Tony Waltham: Retired Senior Lecturer, University of Nottingham, UK, Award-Winning Geologist, Author, and Lecturer
Tuesday, January 13, 2026, 3:00-4:00 pm
To be followed by informal discussion
Koffler Great Room at ASA and Zoom
In the second of his lectures, Tony Waltham will take up regional subsidence, a topic of concern to all the great coastal cities of the world—as well as inland cities such as Phoenix AZ. Subsidence, where a large part of a city slowly descends to lower levels, is almost always due to excessive groundwater extraction, with declining water tables. Dr. Waltham will explain how water abstracted from beds of sand drains water from adjacent beds of clay. The clays then compact, with the extent of ground subsidence depending on the clay type, its thickness, and the amount of water table decline. Mexico City holds the records for the amount of subsidence, and Jakarta currently has the greatest rate of sinking. Interestingly, Venice has subsided very little, but its critical position virtually at sea level has demanded unusual remedies and expensive engineering works.
Photo Credit: Dr. Tony Waltham
Photo Credit: Dr. Tony Waltham