Leveling survey near South Sister, OR

Leveling crew near South Sister volcano, Three Sisters Wilderness, Oregon USA. A surveying instrument called a level scans a barcode pattern on each of two staffs (inset) to measure the precise elevation difference between ground points. One staff is moved ahead and the process is repeated until a permanent benchmark is reached and its elevation relative to a starting benchmark is established. Leveling surveys helped scientists track an episode of surface uplift centered near South Sister that began in 1998 and continued through 2017 at a gradually declining rate. USGS photograph by Michael Poland.