Why does the Reykjanes Ridge lack a rift valley despite spreading slowly?

The Reykjanes Ridge is an exception to the general rule that slow-spreading oceanic ridges feature a rift valley. While most ridges spreading at rates of 20 mm (0.8 inch) per year or less typically exhibit a fault-controlled rift valley, the Reykjanes Ridge lacks this feature due to the influence of a hot spot located directly beneath the spreading centre.12

In standard geological models, slow-spreading ridges are characterized by rift valleys because the crustal plates are under tension, leading to block-faulted topography. However, the presence of a hot spot introduces significant thermal and volcanic activity that alters the ridge's morphology, effectively preventing the formation of the characteristic rift valley despite the slow rate of plate divergence.231