Pop Up Meaning

(idiomatic) To appear without warning.

Example: To come up with a "pop" sound.
  The toast is in the toaster - when it pops up it will be ready.‎
2013 June 21, Chico Harlan, “Japan pockets the subsidy …”, The Guardian Weekly, volume 189, number 2, page 30:
  Across Japan, technology companies and private investors are racing to install devices that until recently they had little interest in: solar panels. Massive solar parks are popping up as part of a rapid build-up that one developer likened to an "explosion."
  I can't remember where I left my keys, but they normally pop up somewhere.‎