This mountain looks vaguely like Mt. Fuji. Seeing that Mt.Fuji is about 3,776 m tall, we will be using this value as a referece.
3776m = 128px as shown in picture. This represents the height of the mountain.
300px/128px = 2.34375 (ratio of width and height of mountain)
3776*2.34375 = 8850m
Using the volume of cone, we get a value of...
7.74e10 m^3, or 7.74e16 m^3
You can see on the third picture on the link above that the mountain is pretty much obliterated. We will go with violent fragmentation for this one.
Now for a low end: (Violent fragmentation)
7.74e16 * 69 J/cc = 5.341e18 J, or 1.28e9 Tons TNT
Now for high end: (Pulverization)
7.74e16 * 214 J/cc = 1.656e19 J, or ~4e9 Tons TNT
Both of these values end in High 7-A, or Large Mountain level
Here is the result:
A mountain level feat for a destroying a mountain. Why am I not surprised.....?
This is a destruction feat, not a speed feat. There is no need to find the actual distance between the girl and the mountain, as the height of the actual mountain is already given.