  We report the first observation of seasonal modulations in the rates of
cosmic ray multiple-muon events at two underground sites, the MINOS Near
Detector with an overburden of 225 mwe, and the MINOS Far Detector site at 2100
mwe. At the deeper site, multiple-muon events with muons separated by more than
8 m exhibit a seasonal rate that peaks during the summer, similar to that of
single-muon events. In contrast and unexpectedly, the rate of multiple-muon
events with muons separated by less than 5-8 m, and the rate of multiple-muon
events in the smaller, shallower Near Detector, exhibit a seasonal rate
modulation that peaks in the winter.
