What are the signs that a super volcano may be under Yellowstone National Park?

Answer 1

The area is volcanic, and there's the hot geysers. These show the crust is not so deep there.
Then, geology might show previous vulcanism in the zone (some millions of years before would suffice).

Answer 2

The Yellowstone Caldera

"Yellowstone National Park in Wyoming, USA is a haven for vacationers and tourists coming to appreciate the area's rugged natural beauty. It is also an attraction because of its mysterious volcanic activity. In the last 50 years scientists have been closely studying the volcanic activity in the Yellowstone area to understand the source of this smoldering cauldron and how it has behaved in the past. By studying the pattern of eruptions in the past, scientists hope to predict what it will do in the future.

Scientists estimate that approximately 2.1 million years ago the first large caldera-forming eruption occurred in the Yellowstone area. From the evidence they have gathered it appears there have been three such cataclysmic eruptions in the Yellowstone area in the last 2.1 million years, each occurring at intervals of 600,00 to 800,00 years apart. The most recent eruption in the Yellowstone Caldera occurred 640,000 years ago.

According to the U.S. Geological Survey…
"The three caldera-forming eruptions, respectively, were about 2,500, 280, and 1,000 times larger than the May 18, 1980 eruption of Mt. St. Helens in Washington State. Together, the three catastrophic eruptions expelled enough ash and lava to fill the Grand Canyon."




The initial eruption of 2.1 million years ago was 2,500 times more powerful than the Mt. St. Helens eruption and perhaps was the largest, most violent volcanic eruption in the history of earth. Enough ash and volcanic debris exploded from the eruptions to cover the entire western half of the United States with about a four-foot deep layer of ash. Roughly 600 cubic miles of material were thrown into the atmosphere. Unlike many of the world's caldera-forming volcanoes that are found over subducting tectonic plates, the Yellowstone Caldera is fed by what geologists call a hotspot beneath the crust. This is the theory that explains how volcanic activity can occur in the middle of tectonic plates, away from geologically active plate margins.

An enormous magma chamber 40 by 80 kilometers lies in wait beneath the giant Yellowstone Caldera. Scientists have recently surveyed the ground in the enormous caldera and have found the ground seems to be bulging upward, indicating the magma chamber is on the move. Since there are no historical precedents for this type of eruption, scientists do not know how to predict if a giant caldera-forming eruption will occur again. One thing they do know is that the Yellowstone eruptions were far, far more powerful and violent than the Toba eruption of 74,000 years ago. If the Toba eruption could reduce the human species to a few scrappy survivors, can you imagine what another eruption of the Yellowstone Caldera could do to us?

http://www.extremescience.com/calderas.htm

Answer 3

There is a dome forming in the area of yellowstone lake, and the lake itself is starting to tip causing previously forested shorelines areas to flood.

Also when viewed from space, an area within yellowstone, about 60 miles in diameter has the same appearance as other volcanic calderas in other parts of the world.

Answer 4

There is a massive caldera under Yellowstone. It has erupted in a "Super Eruption" in the past.
Ash layers from the past have been found around Yellowstone.