Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: The principle of uniformitarianism states that most of the landscape of Earth was formed slowly and over a long period of time. Which occurrence of Earth is least supported by this principle?
volcanic eruption
Sudden formation of a mountain range.