The three stamps belong to a set of five issued on the 5th of June 2003 and picturing volcanoes. The three volcanoes that are pictured on those stamps are (from top to bottom) : Ruang, Tambora and the famous Krakatau (or Krakatoa). The two other stamps of the set picture the Merapi and the Kerinci.
The five stamps have also been issued in sheet containing two of each stamps and two labels. I could not find a scan of the complete set or of the sheet, so I can not show it to you. Sorry. Indonesia is the country with the greatest number and density of active volcanoes. Indonesia usually is a the top of the statistics for active volcanoes, eruption and unfortunately, fatalities due to volcano ! Just look at this map of the volcanoes located in Indonesia and you will understand.
I like this cover. The shape of the stamps is rather unusual and quite well appropriate for the subject. The cancel is very clean and neat. It seems to come from a philatelic bureau, so this must not be a surprise.
Volcanoes on stamps must be a very interesting topic to collect….
By the way, following some questions I got recently : if you are interested to get a cover or a set of stamps that I show on my blog, then just send me a mail to firstname.lastname@example.org and we will see what we can do. Thanks.