Virtual Memory Usage Exceeding Physical Drive Space

I have a machine running Ubuntu on Amazon EC2. The machine has a 43 Gb root drive and 30 Gb of RAM. I am running a processor and memory intensive process and I've noticed that it sometimes stalls for no apparent reason. I'm looking at the system usage via the htop program. I've included a screenshot below. Does it make sense that the VIRT column adds up to more than the physical drive space of the system? My understanding is that is virtual memory usage. Essentially I'm trying to understand whether my process is freezing because it's running out of resources, and which resources it's running out of.