This is a type of Hawaiian lava called pahoehoe.  As you can see, it's kind of blobby and ropy at the same time.  The lava is thick enough, even when hot, that it can pile up into these forms.  It will form all sort of bizarre patterns that can be quite interesting.  The surface of the lava is quite irregular, so one has to be careful when walking across it. 

There is another type of lava, A'a (pronounced ah-ah) which is irregular, sharp, and jagged that would truly hurt if one were to fall on it.  A'a might be the sound one makes after falling on it, who knows.  Lava is very tough on one's boots.  After a few days of walking on lava, they looked like they had aged a few months.