It comes ten years after a massive ash cloud drew air travel to a standstill.
There have been small earthquakes and an ‘inflation’ on Mount Thorbjorn, which looks over the town of Grindavik.
The Icelandic Met Office declared a state of uncertainty, while alerts for aviation were raised from the standard ‘green’ to the more alarming ‘yellow.’
Famously in 2010, eruptions at Eyjafjallajokull meant a huge ash cloud rose over north Europe.
More than 100,0000 fights were cancelled and around eight million air travellers were stranded.
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But the rise could be due to tectonic activity, which suggests a powerful earthquake might be on its way.
Pall Einarsson, professor of geophysics at the Faculty of Earth Sciences at the University of Iceland, told AFP: “It’s too soon to try to distinguish which (scenario) is the most likely.”
Rognvaldur Olafsson, chief inspector at the Department of Civil Protection and Emergency Management, said via AFP: “We always have to plan for the worst, so we are planning for an eruption, but the most likely scenario is that this event will just stop.”
As a precaution, measuring instruments were due to be installed on Monday.
It would be a historical event.
The last eruption on the Reykjanes Peninsula took place around 800 years ago.
But Einarsson stresses that eruptions in this region of Iceland are “effusive”.
This means there is such a narrow flow of lava and a small amount of ash there is not much chance of harming people.
It comes as the Taal Volcano is thought to be on the brink of eruption.
The Philippines volcano has been put on Alert Level 4.
Officials expect “hazardous explosive eruption is possible within hours to days”.
On Friday, January 24, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said of lumes of steam and smoke emanating from Taal’s main crater.
As of midnight GMT (8am local time) the volcano has ben spewing a tremendous 268 tons (224 tonnes) of toxic sulphur dioxide (SO2) into the air.
An official Taal Volcano bulletin reads “For the past 24 hours, the Taal Volcano Network, which can record small earthquakes undetectable by the Philippine Seismic Network (PSN), recorded 486 volcanic earthquakes, including four low-frequency earthquakes.