More about these later. The USGS photo-archives are probably one of the best sources of information. Go there for photographs of various types of volcanoes. Their Mt. St. Helens slide set is excellent . In fluid magma eruptions, gas can exolve and escape relatively easily.
Fluid flows are usually basaltic.
Difference between aa and pahoehoe is that aa is more viscous. Eruptions can fountain if there is a lot of magma, but not really dangerously explode. Lava collects at the bottom of the cone and forms a flow. Cinder cones are piles of vesicular material where the blobs of lava froze in the air before reaching the ground. Thus a flow was unable to materialize.