Magma flows easily when it is low in a material made of oxygen and silicon.

Magma flows easily when it is low in SILICA. Silica, also called silicon dioxide is made up of two atoms of oxygen and one atom of silicon. Silica is the most abundant element in the earth's crust and it is the principal component of most sands. Silica is most commonly found in nature as quartz, the two other crystalline forms are tridymite and cristobalite.

Freckles, hives and blisters seems right.