Trench warfare was a crazy thing back then. Read this
on how the Allies set off one hell of a huge boom:
http://en.wikipedia.org/wiki/Battle_of_Messines
While determining the power of explosions is difficult, the 1917 Messines mines detonation was probably the largest planned explosion in history prior to the Trinity atomic weapon test in July 1945 and the largest non-nuclear planned explosion before the British explosive efforts on the Heligoland Islands in April 1947. With approximately 10,000 killed, the Messines detonation is history's deadliest non-nuclear man-made explosion.