No, an "imminent" volcanic eruption is not a plausible explanation. But geological tremors are.
While Yellowstone geological activity is increasing, an eruption is not expected for a very long time.
The animal exodus could also just be migration - however, the video shows the animals running, not walking. Annual migration involves a lot of walking. Running is energy intensive and requires urgency.
From Snopes.com:
As Al Nash, chief of public affairs for Yellowstone, explained in a rumor control video on this subject:
We do have bison, elk and other animals that have moved outside the park recently, but they're doing that because it's the depth of winter, food is a little hard to find in places inside Yellowstone, and they tend to migrate at this time of the winter outside the park to lower elevations where they think there might be something to eat that's easier to get at. When the snow melts off and things start to green up, those very same animals will walk right back into the park.
The animals may have been running in response to tremors; it's normal for animals to be much more sensitive to natural things. However, an increase in tremors doesn't necessarily mean an imminent eruption and Theres nothing about the evidence presented in the Yellowstone claim that shows why the Bison are running. Some parts of the scientific establishment claim that it has not been proven that animals can sense earthquakes before humans can, yet there is millenia of anecdotal evidence that animals can indeed do so, and acceptance of the idea in naturalist circles. National Geographic, for example, contrasts with points of view published in Scientific American.
Yellowstone, a bit like Hawaii, is on a hotspot. Hawaii is constantly active because the crust is so thin. In continental Yellowstone, the energy/pressure has to build up a lot before it blows through the crust - and then it will be an enormous release of energy. Previous eruptions have been quite regular, and thats the basis for predicting future eruptions.
