  We investigate the onsets of three consecutive coronal mass ejection (CME)
eruptions in 12 hours from a large bipolar active region (AR) observed by SDO,
STEREO, RHESSI, and GOES. Evidently, the AR initially had a triple-decker
configuration: three flux ropes in a vertical stack above the polarity
inversion line (PIL). Upon being bumped by a confined eruption of the middle
flux rope, the top flux rope erupts to make the first CME and its accompanying
AR-spanning flare arcade rooted in a far-apart pair of flare ribbons. The
second CME is made by eruption of the previously-arrested middle flux rope,
which blows open the flare arcade of the first CME and produces a flare arcade
rooted in a pair of flare ribbons closer to the PIL than those of the first
CME. The third CME is made by blowout eruption of the bottom flux rope, which
blows open the second flare arcade and makes its own flare arcade and pair of
flare ribbons. Flux cancellation observed at the PIL likely triggers the
initial confined eruption of the middle flux rope. That confined eruption
evidently triggers the first CME eruption. The lid-removal mechanism instigated
by the first CME eruption plausibly triggers the second CME eruption. Further
lid removal by the second CME eruption plausibly triggers the final CME
eruption.
