This pose is Buddha in the position of touching the earth or, calling the earth to witness. It represents an important event in the life of the Buddha.
About to reach enlightenment, Mara, the demon, and his three daughters arrive to try and seduce the Buddha into a life of sin.
When the soon-to-be Buddha touched the Earth with his right hand, the Goddess Phra Mae Thorani appeared in the shape of a young, beautiful woman. By wringing the waters out of her long hair she drowned the armies of Mara, allowing the Buddha to continue meditating and reach enlightenment.