This is a 'lava tree', where the lava flowed around a tree, hardened, and flowed away. A Puka is the cavity the shape of the tree that is left when the lava stays and burns the tree after it hardens.
'I fell into a puka (poo-kah) the other day, but I climbed out' said a child of a friend in Puna. A puka is a hole in the ground that is covered by plant life on top that cannot support weight. The hole can be twenty-five feet deep; it is left when lava cools around water-rich trees, hardens, and then burns the tree. There is property across the street that is for sale, but is not worth anything, because the land is full of these holes, and it is unsafe for walking or gardening. Here is a link to understand more, if you are interested: http://www.instanthawaii.com/cgi-bin/hi?!4anXdfjQKS3TrAAuT8fOIMn9r47N8S2fTbr1ooebmzbm0sea8fboR2gbuoermr05rt7MO5bTTjn1TlfdIMOpn0asvibET2EuuemOnCnmusjaOdboRbg1Nomemzbm04
Another part of Hawaii that is little known are the singing snails. They live in the trees in Oahu, and I actually saw them sing in the in-flight entertainment. It is a breezy, flute sound that is hauntingly beautiful. I looked on YouTube, but couldn't get anything but a horrible cannabilization of one by an imported snail. I turned it off right way--don't look at it. It's the ecogeeks one. Here are some articles though that might interest you on the subject:
Here is the man that was in the in-flight movie: http://hanahou.com/pages/magazine.asp?Action=DrawArticle&ArticleID=961&Page=2
The last is simply incredible! Did you know there are spiders in Hawaii that are native to the islands that have Happy Faces on them? I kid you not!
Here is a picture from National Geographic:
And a link to more images:
So--if spiders can smile (and no, they are NOT POISONOUS!)-- so can you!