_Volcanic or lava domes are formed by relatively small masses of lava too viscous (thick) to flow any great distance. Once they erupt to the surface, the lava piles over and around its vent. A dome grows largely by expanding from within. As it grows its outer surface cools and hardens, then shatters, spilling loose fragments down its sides. Some domes form craggy knobs or spines over the volcanic vent, whereas others form short, steep-sided lava flows known as "coulees." Volcanic domes are often found inside the craters of larger composite volcanoes like the one shown growing inside Mt. St. Helens' crater (on the left)
Click on the video to the right to see time-lapse photography from 2004 to 2008 showing the growth of Mt. St. Helens' lava dome.
4. Lava Domes (Notes)
a. Made of single mass of lava too viscous to flow outwards i. Often no layers b. Piles up from vent to form dome c. Can form inside crater of stratovolcano d. Very small e. Ex. Mt. St. Helens