Scripture claims the earth was formed out of water (see Gen 1:2, 2 Pet 3:5) and that once God formed dry land, these waters were "gathered in one place" (Gen 1:9). This "one place" was under the surface of the earth as we see in Gen 7:11 that the major source of the flood waters came from under the earth, not from above it. Dr. Walt Brown, a creationist and a scientist, proposed his Hydroplate Theory in 1980 which hypothesized that huge amounts of subterranean water not only accounted for the Genesis flood, but also provided the mechanism for tectonic plate movement. Despite being ridiculed for basing his scientific theory on "a few obsure passages" in the Bible, it would appear both Dr. Brown and the Bible have been vindicated by science. His astounding book "In the Beginning" can be read online here.
Click here for the news article on the discovery of these vast water chambers and click here for an old wiki article lambasting the idea.