Portland is slowly sinking, new study shows

Portland's land is sinking at an alarming rate, with a recent study indicating that over 80% of the city experiences measurable subsidence at about 2 millimeters per year. This silent risk threatens urban infrastructure, causing issues such as cracked roads and destabilized buildings. The study identifies tectonic activity and sediment compaction as the primary causes of subsidence in Portland, differing from other cities where groundwater pumping is a major factor. Engineering geologist Bill Burns warned that the region's volcanic soil, rich in clay, can shrink when dry and expand when wet, complicating structural integrity. He highlighted that while subsidence is serious, the most significant threat remains from earthquakes, which can cause much larger ground movements.

The study underscores the need for cities to incorporate subsidence into their planning and zoning strategies. Adaptation measures might include raising roads and implementing green infrastructure solutions. As more than 33 million people in the U. S. live in subsiding areas, the implications of these findings are far-reaching.