What causes the separation needed for an oblique shock on a wing? Oblique shock waves form because :

"An oblique shock wave is a shock wave that, unlike a normal shock, is inclined with respect to the incident upstream flow direction. It will occur when a supersonic flow encounters a corner that effectively turns the flow into itself and compresses." - Wikipedia.

For an oblique shock to form, there has to be an angle which makes the flow turn. If you imagine a plane going from Mach 0.5 to 1.0 for example, it's possible for a lambda shock to form. My question is, what causes the angle (provided by separation) for the oblique shock? In the second part of the lambda shock, the first shock causes the separation needed. For the very first part of the lambda shock, there is no shock upstream for the separation to happen.

I'd imagine that it starts out as a normal shock, then turns to an oblique shock with varying speeds. The thing is, there is nothing taking the normal shock (that is now the oblique shock) that was there away. Another way to think of it : If there isn't a normal shock first, what is going to cause the separation and angle for the oblique shock to form? After the oblique shock forms, what will make the normal shock go away? This answer and its comments has some really good info, but (for me) it didn't explain this part.

(I'm usually bad about doing prior research to questions, but this time I did a fair amount. If I missed any sources that explained this, let me know!)