https://en.wikipedia.org/wiki/Lake_Toba
Sinabung is only 25 miles away from the supervolcano Toba.
It makes you wonder if they share the same magma pool at some depth?
Here are a number of photos of this classic Fuji shaped volcano, and a few maps and links to other volcanoes.
https://www.google.com/search?q=mount+sinabung&biw=1600&bih=775&tbm=isch&tbo=u&source=univ&sa=X&ei=F7uHVfDnEpe0yATkhrbICw&ved=0CDIQsAQ