What type of technology is used to obtain data of the inside of a volcano?

What type of technology is used to obtain data of the inside of a volcano? Please give me links not answers.What type of technology is used to obtain data of the inside of a volcano?
A most excellent request.



http://volcano.und.edu/



http://volcanoes.usgs.gov/main.html



http://www.geo.mtu.edu/volcanoes/



http://www.volcano.si.edu/



I think that this should answer your questions. If you have more questions, you can email me. That is if Yahoo answers works like it I think it does!! :-)