Nick, that's not a valid comparitive example. The erosion that created the Grand Canyon is an extremely slow process that is not visible to the naked eye - thus is open to interpretation.

Here, you see the new land being formed right in front of your eyes. You can watch the lava snaking over older, cooled lava from previous eruptions. You look at it, then look up at the side of the mountain and see the very same processes created the entire 10,000' mountain rising above you. And the 20,000' more of mountain below you as it extends down to the ocean floor. And the other 18 islands and atolls that make up the Hawaiian Archipelago.

It's happening now, today, right in front of you. Only one interpretation is possible - this has been going on here for millions of years. No speculation or illogical leaps of faith are required - only eyesight and common sense.