Here I will put a few ideas down about natural phenomena that are difficult to impossible to explain by the creationist hypothesis.
Limestone caves: Many creationists assume that the earth is young, less than 10,000 years, and that geological features are explainable by the "flood". How could limestone caves form in a flood? That's presumably easy - by rapid erosion - but then the intricate layered forms in the caves are hard to explain. The more difficult question to answer is: how did the stalactites form? The rate of deposition is measurable. Just how old are they?
Ice and other layers:
Radioactive dating: "Radiometric Dating: A Christian Perspective" by Dr. Roger C. Wiens, Division of Geological & Planetary Sciences, California Institute of Technology.