Is lava always liquid?

We have all watched on TV images of liquid lava rushing down the slopes of a volcano. But all lavas are not liquid; some are more viscous and flow down as honey would do. Other lavas are even thicker, and practically do not flow at all. These types of very viscous lavas are the most dangerous because they just pile around the volcano’s vent, which builds great pressure inside the volcano and causes explosive eruptions(like the Merapi, in Indonesia).