On this page of our game guide to Batman: Arkham Knight we explain how to investigate the unusual seismic activity on Miagani Island.
Call in the Batmobile and drive toward the central part of Miagani Island. When you get close make sure there are no tanks or enemy flying machines in the area (if there are some, you have to deal with them first). Park the Batmobile in the designated spot and watch a short video warning you against enemy military forces closing to the Botanical Gardens. Your next objective is to protect the Poison Ivy and her plants.