You will be given a definition of a task first, then some input of the task.
In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 

Water flows by rocks. Chemicals are in the waters. Chemicals react with rocks. Rocks change to a different kind of rock. Oxygen in the air reacts with rocks. Rocks change to a different kind of rock. 
Output:
What happens during chemical weathering?