Why is my LND node closing channels? I have noticed when running lncli closedchannels, that I have some channels that are closed by my node (close_type: local_force_close).

I am quite sure I have not initiated this manually myself. Is there some logic in LND that drops some channels?
Many! 

If you look at the BOLTs ( lightning RFC) you will find many situations in which nodes must fail a channel (meaning a force close) if something happens in an unexpected way while communicating with a channel partner. This could be even as easy as an unresponsive channel partner while settling an htlc in which case you have to settle the htlc onchain. But there are many more conditions in which the protocol asks to fail the channel.