how can i create a thick terrain

like this

Uggh, why is the picture not showing up?

use the blizzard cliffs increase 1 or 2 on the entire map to make the ground thicker

but the sides will also be flat

ok make the map with shallow or deep water as the initial height
use blizzard cliffs rise 2 on the entire map
lower to form a pond like thing in the image using lowering tool
read this
hope it helps