premise: Cape Verde is a volcanic archipelago situated above an oceanic rise that puts the base of the islands 2 km above the rest of the seafloor. Cape Verde has been identified as a hotspot and it has been argued that a mantle plume might be underneath it causing the volcanic activity and associated geothermal anomalies.
hypothesis: Scientists understand everything about Cape Verde.
reason: It said that people are arguing that a mantle plume MIGHT be under it. It was clear that they were not 100% sure of what was going on. If they are arguing and say something might be there, then there is not total understanding.