Icelandic Streams: level with their banks?

I visited Iceland last May, and among the many fascinating sights, I noticed that most of the little rivers that wind through the countryside had cut no valley into the ground. The water was, as I said in the thread title, level with the land around it.

Geologically, what does this mean? That these are very young streams, or that the volcanic earth is very hard and resistant to erosion? Or something else?

Over 50 views, and no one knows the answer (or cares to share it)? I find that difficult to believe.

I can think of several possibles but since I am not a geologist I will be wrong.

Iceland is active volcanically straddling the North Atlantic plates, the result is that there are lots of fresh lava flows, some acually underneath the ice which melts and causes epic floods.

It may be that those rivers you saw are in a region where the surface is replaced by fresh lava flows so frequently that erosion does not have much of a chance to take place.

Since you were there in May, during spring thaw, it sounds like one or more of the following:

[li] The runoff may have raised the water levels to fill the riverbed completely.[/li]
[li] These may have been transient rills, that exist only when there’s excessive runoff. They don’t follow any regular path, they just meander over the surface like a drizzle of tap water on a dinner plate.[/li]
[li] The top layer of the soil may have become frozen, and then thawed in the spring to become boggy or even swampy. Thus the soil and the water would seek similar levels.[/li]
I’d be most inclined to the first explanation, but wouldn’t be surprised if there were something related to the island’s vulcanism that would give another reason.