Mine Sweeper

Step 1: Open FireFox/IE
Step 2: Go to www.youtube.com
Step 3: Open 20 videos (or more if you have a high speed internet connection)
Step 4: Go to the mine field, get on your epic mount, and just run around the mines, they'll all blow up at the same time once the ping gets to you.

Worked perfectly for me, unfair way to do it but eh.

I just tested this, and it's actually absurdly easy, though it is possible it was changed in one of the most recent builds from what you saw.

You don't need to actually hit the mines continually. Considering the mines themselves won't activate before you hit the ground, there is a very small grace period built in to the timer of the achievement. To get it, simply go to the center of the field, and start running into mines. As soon as you land, sprint to the nearest mine by where you landed, and you'll continue your chain.

Hitting multiple mines at once counts. I got it in four jumps for hitting one, then three, then four, then three again.

The Minefield is located southwest of K3 in The Storm Peaks, around 36.86.