There's a specular light positioned above the terrain, which adds the sparkle (light3 in https://github.com/felixpalmer/lod-terrain/blob/master/js/sh...). If you want to play around with changing the light etc, you can use Mozilla's awesome in-browser GLSL editor (currently in FF beta): https://hacks.mozilla.org/2013/11/live-editing-webgl-shaders...