With each large earthquake, ground shaking causes additional collapse within the Pu‘u ‘Ō‘ō crater, sending a plume of reddish-brown ash skyward. The size and vigor of a plume depends on the size of the earthquake and subsequent collapse. This roiling ash plume followed the magnitude-6.9 earthquake on May 4. Much of the rock within the crater is rust in color, which is a result of heavy alteration by acidic volcanic gases. When the rock is pulverized by a collapse event, the resulting ash plume is pink to reddish-brown ash plume. USGS photo by T. Neal.