Some who attack the idea of a Global Flood based on the claim that the Flood had to go as high as Mt. Everest sense all the Mountains were covered . Mt. Everest peaks at 29,035 feet, and there is not enough water on Earth to cover it such a depth. This is actually a straw man argumant since no creationist claims that the Flood covered Mt. Everest at its current hight. Further more like many other such claims the Bible answers it.
This passage shows that mountains rose and valleys sank during the Flood. The result is that Mt. Everest rose up during the Flood so the Flood did not need to be any were near that high.
There is enough water on Earth for a Global Flood. If the Earth were smoothed out, the water in the oceans would cover the Earth to a depth of about 8,813 feet. This figure does not include the water in rivers, lakes glaciers and other sources. They would add about another 2-3 thousand feet. In reality the Flood would really only need to be a little over 7,000 deep.
So real question is whether or not it is possible for Mt. Everest to have roses to its current hight fast enough to have raised in a time scale consistent with the Flood. The earthquake that caused the Indonesian tsunami of December 26, 2004, caused an uplift of at least 20 feet in a few minutes, which is a speed of about 240 feet per hour. At that rate Mt. Everest have reached 29,035 feet in about 5 days. So forces actually observed in Earthquakes are sufficient if extended long enough to quickly raise even the highest mountain in world to its current hight is just a few days.
The result is that based on the amount of water on the Earth and fact that observed tectonic forces have the potential to quickly raise mountains, that the Global Flood of the Bible is at least theoretically possible.