Age-ude-uke (Rising-forearm-block): is one of the first blocks you learn in karate. The nature of age-ude-uke is that it travels in an upward direction, and is the perfect block against punches to the face, or downward attacks to the head and face (for example like is someone was going to hit you on the head).
 

Stage 1: Make your prepare, as shown.

Stage 2: The preparing hand begins to pull back to the hip (hikite), while the other arm begins to travel across to the centre of the body, ready to travel upward.

Stage 3: The returning arm draws closer to the hip; the blocking arm travels further upward.

Stage 4: Upon finishing the block the blocking forearm rotates 180 degrees (or thereabout).