Figure 1 (IMAGE) American Physical Society Caption Mount Rinjani, Indonesia, 1995 eruption. Visible volcanic lightning can occur throughout the plume, invisible sparks may occur in the low- pressure region of standing shock waves formed in the near-vent region. Credit Oliver Spalt CC-BY-SA 3.0 Usage Restrictions Use with appropriate credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.