(Meredith) -- In Spain, thousands of people in La Palma are wondering if and when they will be able to return home.
This video -- recorded by the Geological and Mining Institute -- shows how lava is moving on top of lava that spilled out previously.
A geologist from the Spanish National Research Council explains that this creates a cold crust on the surface. Authorities are also tracking lava flowing from the volcano towards the Atlantic.
If molten lava reaches the sea, it can create dangerous chemical reactions and toxic gas.