Before erupting, volcanoes like Kīlauea physically swell and expand as magma builds pressure underground, much like inflating a balloon.

Volcanic inflation is a measurable geological phenomenon driven by magma moving into a volcano's plumbing system. When a magma reservoir fills, it exerts immense pressure on the surrounding rock, causing the surface to bulge outward and tilt away from the center of inflation. The U.S. Geological Survey (USGS) monitors this process using high-precision GPS and tiltmeters that can detect changes as small as one microradian.The 2018 eruption of Kīlauea on Hawaii's Big Island provided a dramatic example of this cycle. Between May and August 2018, magma drained from the summit reservoir to the Lower East Rift Zone, causing the caldera floor to subside significantly. This event produced 62 major collapse events recorded by the Hawaiian Volcano Observatory as seismic activities equivalent to magnitude 5.3 earthquakes.By the end of the 2018 sequence, the summit had dropped approximately 1,600 feet, drastically altering the landscape of Hawaii Volcanoes National Park. This subsidence occurs because the magma chamber's roof loses structural support once liquid magma exits through eruptive vents. Understanding these patterns of inflation and deflation allows volcanologists to forecast potential eruptions and issue timely evacuations for nearby communities.