Highly viscous lava can accumulate over a vent instead of travelling far, producing a lava dome. The rocky mound at Novarupta is a useful contrast with the flowing lava that builds a broad shield.
Look for a compact, rough-sided mass rather than expecting a smooth half-sphere. A dome may form within another volcano’s crater or as a separate feature. Its shape explains resistance to flow; it does not imply a harmless eruption. Domes belong here because volcanoes can contain smaller volcanic structures.
Source / photo: USGS · Public domain. Resized. No claim to original U.S. Government works.