"to run away," 1861, American Civil War military slang, of unknown origin, perhaps connected to earlier use in northern England dialect with a meaning "to spill." Liberman says it "has no connection with any word of Greek, Irish, or Swedish, and it is not a blend." He calls it instead an "enlargement of dial. scaddle 'scare, frighten.'"What I discovered is that it's a compression of the phrase "Let's get out of here." I discovered it by saying it quickly and interacting with someone who didn't at first catch what I'd said.
By the way, the phrase "Let's get out of here" is extremely common, and I heard, back in the 70s, that it actually is spoken in every single movie. I don't know if that's true, but it was a folk belief that interested me, and I've seen a lot of movies since then, and it might be true.
ADDED: Here's the OED's effort at etymology:
‘Said to be of Swedish and Danish origin, and to have been in common use for several years throughout the Northwest, in the vicinity of immigrants from those nations’ (Webster, 1864); but there are no forms in Swedish or Danish sufficiently near to be seriously taken into account. There is some slight evidence of the currency of the word in English and Scottish dialect use before it became prominent in America, but it is doubtful how far this is of importance for its origin.