To begin with, it is both! I have an absolute passion for geology, particularly, paleontology. However, there are many practical applications for geology that I suspect many might not even realize, or have stopped to consider as we go through our day-to-day activities.
Geologists study the behavior of earthquakes, and volcanoes to gain a better understanding of how they work so that they can more accurately predict when a volcanic eruption, or an an earthquake will occur so that communities can be warned, and take what action is needed to protect their citizens. Accurate prediction of these natural events is still a work in progress, but as we continue to study these events, and processes, the better our understanding will be, and therefore our ability to predict their behavior becomes more possible.
Global climate change is a biggie today, as we continue to seek out just what role humans play in changing climate, what, if anything can be done about it, and how to adapt to coming changes.
Geologists play a huge role in fossil fuel exploration, and exploitation. This will be a continuing area of importance even as we seek out alternative, renewable sources of energy. Mining geologists play pivotal roles in the mining of important mineral resources as well.
Structural geologists play a key role in determining the viability of the substrate on which mega-structures are built, such as skyscrapers, dams, nuclear power plants, bridges, etc. Imagine building something as massive as the Hoover Dam on shaky ground, a catastrophe in the making.
What have I left off the list? What else can you think of, and if this is something you have not thought of before, I am challenging you to do so now, and next time you run into a geologist, be sure to think him, or her for many of the things that up until now, you might not have thought about, or took for granted. =)