How deep do your roots go?

Giant California redwoods are not as strong as you might think, but are in fact vulnerable to being blown over because their roots are relatively shallow. The danger to them is so real that public access to them is often restricted to prevent people clambering over the roots and loosening the soil around the base of their massive trunks. You wouldn't think that was possible, but apparently too many visitors may weaken the root system and the next gale may bring them down. It is an interesting...