In the interest of narrowing questions down, I am splitting these into particular elements and element combinations.
In summary, Ley Lines have just become active again on Modern Earth, and are wreaking natural and unnatural havoc on the world.
This question will focus on the Water ley lines, and their interactions with the world around them, including the interaction between Water and the other 3 elements not yet covered: Air, Earth, Wood. Ley lines are not restricted to a particular area, but exist across the entire world. Some places have denser concentrations than others. (Interactions with Fire are covered here).
What are catastrophes that could be caused by very high volumes of Water magic going rampant, and clashing with other elemental magics also going rampant? Again, this can be of any scope, as long as it does not result in a mass extinction event. And I'm quite okay with every combo not always producing the same results.