What were to happen if I short-circuited electricity generated by a power plant to the Earth?
In Single Wire Earth-Return systems, the earth is used as the return wire. 

If the soil conditions, hydrogeology etc. are up to it, you could get quite a large return current, which would blow breakers. If the soil is really dry (think desert and sand) then maybe not much current would flow (depending on whether your 'stake' is hundreds of meters long or not, and if it reaches any underground water). 

Unless there's some great anomaly in the earth conditions (assuming homogeneity in the earth conditions) the volts per meter will not likely be very large, so I don't see much in the way of hazards. Maybe it would make the nightcrawlers (worms) come up out of the ground or raise zombies or something.