What we can expect in El Hierro
Iceland is part of the Mid-Atlantic Ridge, and is the only piece of land that has emerged from a mid-ocean ridge anywhere in the world, because it is right on top of a hot spot. The Canarian volcanism is more complex, but if one thing is clear, it is that the activity is a result of oceanic island intraplate volcanism on and we can rule out any link with a hotspot. The most commonly accepted theory is that the Canarian volcanism is linked to a process of fracture and thinning of the Atlantic oceanic crust associated with the counterclockwise rotation of the African plate as it collides with the Eurasian plate.
At the start of the eruption that generated Surtsey, the seabed was located about 130 m depth and it was relatively flat. The total volume of ejecta was just over 1 km3 . The eruption lasted for more than 3 years almost without interruption.
In today's eruption of El Hierro, the first crack appeared between the 10th and 19th October 2011 from the spine of La Restinga, running from 900 m below the surface and 5 km from the coast to just 2 km and 150 m in a rugged seabed and steep slopes leading to the deep sea surrounding the archipelago. It is estimated that, together with the second eruptive phase, which occurred between 2 and 6 November 2011, the total volume of ejected material is no more than 100 million m3 , about 10 times less the Icelandic volcano. Let's wait to see if the magnitude of the eruption increases significantly, but so far no seismic precursors appear to indicate.
On the other hand, what now remains of the island of Surtsey is almost exclusively effusive basaltic material. Fragmentary rocks caused by the initial stages of a phreatomagmatic eruption are much less resistant to erosion. If a volcano appears off the coast of El Hierro, the pyroclastic source materials of this type of eruption are going to erode rapidly. If a new Macaronesian island is going to appear, it will require a sufficiently long and productive period of eruption to avoid dissapearing rapidly under the waves again. Something in the order of magnitude that was seen in the eruption of the Westman Islands - the Anglo-Saxon name for the archipelago south of Iceland.
So if the question is whether there will a new island in the Canary Islands, the answer is yes. But if you expected to be a result of this volcanic phenomenon, most likely not, especially taking into account the frequency of glaciations in recent geologic times, the consequent rise and fall of sea level, and variety of seamounts (former islands ravaged by erosion) whose peaks are at depths around 100 meters. But let's face it, we all would love to see and name a new island recently emerged from the depths of the Atlantic.