Why does nose start bleeding at high altitude?

Nose bleeds are obnoxious and embarrassing at times. They seem to happen at just the wrong time like when you are out on a first date or wearing all white. There are a number of reasons your nose might bleed.
Picking your nose will oftentimes make it bleed. High elevation will cause it to bleed too because capilaries bust. Getting socked in the nose is sure to start a nose bleed. Being congested is a common reason for bleeding through the nose as well because the build up of pressure causes capilaries to break.

Nose bleeds are fun but it is better for the blood to come out of your body than it is to go back into it so be sure to let in bleed if it must. Blow out what you can and if it persists, raising your nose up into the air may be the only way you can make it stop but don't let the blood flow back in too much if possible.