It didn't. The Yellowstone volcano last erupted about 70,000 years ago. The last super eruption was about 640,000 years ago.
The Yellowstone caldera is not "overdue" for an eruption. You may have heard that the Yellowstone Caldera erupts regularly every 600,000 years and the last major eruption was 640,000 years ago. In reality the caldera does not erupt regularly and as gone as long as 800,000 years without a major eruption.
There is no record of the Yellowstone volcano erupting on January 12, 2009. The volcano has not had a major eruption for about 640,000 years, but it does experience minor volcanic activity such as geysers and hot springs.
Yellowstone has a approx. 650,000 year-old cycle, and so the last major eruption was about 650,000 years ago. Therefore, the next eruption is long overdue and a major volcanic eruption is expected to occur in this century. It may be late 21st century (2070+), mid-21st century (2040+) or early 21st century (i.e. now or in the next two decades). Basically, Yellowstone will erupt that is a guarantee. Anyone guessing December 21, 2012?
The last super eruption was about 640,000 years ago while the last magmatic eruption was about 70,000 years ago. There is evidence of small steam explosions up to about 1,000 years ago.
Yellowstone's huge magma chamber underground is a boiling river continually building for a major eruption. Scientists estimate the huge eruption will be so great that it could destroy most of the North American continent.
The last major eruption of the Yellowstone supervolcano occurred approximately 640,000 years ago. Since then, there have been smaller volcanic events in the area, but no catastrophic eruptions on the scale of past events.
The last major eruption of Yellowstone supervolcano occurred about 640,000 years ago. There is currently no definitive prediction for when the next eruption might happen. However, Yellowstone is constantly monitored for signs of volcanic activity to ensure early warning and preparation.
Yellowstone Volcano. Some called it Yellowstone Caldera.
The Yellowstone volcano is about 2.1 million years old. It's first major eruption dates to that time. The volcano is the latest in a series that formed from the same hot spot starting about 16 million years ago.
Most scientists believe that Yellowstone is not truly active and that they would be able to detect if the Yellowstone volcano was going to erupt years before it erupted. But there is no way to no for sure if the Yellowstone caldera is truly active (building up for an eruption).
Yellowstone National Park is a super volcano. Yellowstone is over a "hot spot" which is why there are geysers there. The hot spot blew millions of years ago leaving a caldera where the geysers are. Yellowstone is a volcano but do not go expecting an eruption unless you can wait a few million years.