Can a single traumatic event cause profound fear conditioning in the amygdala?

Yes, and it can lead to conditions such as PTSD (post traumatic stress disorder) and phobias. Research has shown that the effects of significant trauma can lead to changes in the brain over time. For example, the hippocampus becomes smaller/decreases in volume in patients with chronic PTSD and there is an increased amygdala response with a decreased anterior cingulated response on functional MRI. These patients can also develop dysfunction of the HPA (hypothalamic-pituitary-adrenal axis). Great question.