“Caves 101” at Thacher Nature Center on Sunday, Jan. 13, at 2:00 p.m. Have you ever wondered: What is a cave? What is karst? How do caves form? And just what is a phreatic tube, anyway? This presentation by Thom Engel will cover everything you always wanted to know about caves, but were afraid to ask. The talk will be minimally technical with only three related chemical equations and one graph plus a lot of pictures. Call 518-872-0800 for more information.