What is the difference(s) between aa and pahoehoe lava?

Question

What is the difference(s) between aa and pahoehoe lava?

Answer 1

Here's the USGS glossary explanations for aa and pahoehoe lava, including pictures.  The most obvious difference is visual (although there are a ton of other differences).  Aa is rough and rocky in texture, whereas pahoehoe is ropey-looking.

http://volcanoes.usgs.gov/Products/Pglos...

http://volcanoes.usgs.gov/Products/Pglos...