Why traffic jams can appear without any crash or lane closure

I've sat in traffic that suddenly slowed to a crawl, then sped up again without any accident, broken-down car or merging lane. It feels like the jam came from nowhere. I read that a single driver braking can cause a wave that travels backward through traffic, but how does that small slowdown become several minutes of standstill? Is there a simple mental picture for how these ‘phantom jams’ grow and eventually disappear?