This guide shows how to install Arch Linux using a USB-Stick. A running U-Boot installation is required, in my case this was U-Boot 2013.04 which came with the original image. Next, I created a memory stick. I followed the documentation of Arch Linux ARM, I just used a USB stick instead of a Micro SD-Card. Now, plug the USB stick into your Beagle Bone Black and press a key to get the U-Boot prompt. U-Boot has the ability to boot from a USB stick, but some custom commands are required. First you need to scan the USB bus system.
U-Boot# usb reset (Re)start USB... USB0: scanning bus 0 for devices... 1 USB Device(s) found scanning usb for storage devices... 1 Storage Device(s) found