Light slowly flashing on external hard drive

A new WD Elements portable hard drive has been plugged into a USB 3 port on a Linux desktop.

The hard drive does not appear on an fdisk -l
listing. The small light on the drive is slowly flashing.

What is happening ? Why doesn't the drive appear in the fdisk listing ?

Is the system trying to automatically mount the hard drive ?

Is the USB port underpowered ?

I hesitate to unplug the hard drive while the light is flashing in case this corrupts the filesystem
on the hard drive.