Re: How long does lava need to cool before I can walk on it?

You could probably stand on most kinds of lava within a day or two of their 
eruption, as long as the volcano is not still erupting.  When lava comes 
out of a volcano, it can be anywhere from 900 C to 1200 C (that’s about 12 
times hotter than boiling water!).  There are four basic types of lava, and 
each one cools at a different rate:  
A’a - a Hawaiian name for a large, thick and chunky kind of lava that flows
      quickly, but also cools quickly in rough chunks. 
Pahoehoe - a Hawaiian name for a smaller, smooth running lava flow that
      takes a lot longer to cool.   This stuff usually cools on the outside
      first in smooth, glassy looking rocks, making a kind of tube that
      lets hot lava inside of it keep running.  
Block Lava and Ryholite Lava are both very thick, slow moving, and fast
      cooling kinds of lava.

With good boots on (some lava cools into very sharp rocks that could cut 
your feet) you could probably stand on most of these types of lava after 
they have been cooling for a day or two.  The big danger is that 
(especially with pahoehoe), if you try to stand on a lava flow, it might 
not be finished flowing, so the lava flowing underneath gives off enough 
heat to keep the hard rock on top of it quite hot.  Another danger with 
pahoehoe is that skylights can form.  These are places where the hard rock 
“tube” may have fallen in and you can actually see the red hot lava running 
underneath it.  While they look VERY cool, they also give off a lot of 
heat.  You also have to keep in mind that lava can release poisonous gasses 
that can make you very sick.  I hope this answers your question.  Here are 
some cool sites for you to check out for more information:

Volcano World 
NASA's Classroom of the Future 
Just for something different, you can also check out a live web cam pointed 
at Washington state's Mount Saint Helens volcano. Web Cam