Redoubt Volcano, in Alaska, is one of the more troublesome volcanoes in the state. Not only is it relatively close to population centers, but it also lies directly within the aircraft corridors above the Aleutians for planes headed to Asia and beyond. This means that USGS and AVO geologists have to be especially vigilant in watching Redoubt's every move.
Currently, the volcano has been recently changed to a yellow (elevated) alert, due to increased steam/volcanic gas emissions (remember, the number one volcanic gas is water vapor) at the volcano. So far, there haven't been any reported eruptions of ash (i.e., juvenile, fresh magmatic material), but you never know how far behind rumblings and steam that could be (well, you can have an idea that it could be "not far"). It has been almost 19 years since the last eruption (see the famous image of the eruption column above) of Redoubt, so we're all on pins-and-needles to see whether this activity will lead to a new eruptive period.