The viking exploring happened during the medieval warm period, during which a lot of the land now considered cold and barren were suitable to grow a few hardy crops and to graze livestock (goats, sheep and perhaps also cows) - this was certainly the case in Iceland and Greenland.

With many skilled sailors, good knowledge of the North Sea, fishermen often blown out of course by storms (and thus tales of birds and cloud formations that could indicate land), the ability to explore was there.

It was primarily the Norwegians that explored the North Sea and settled on Iceland and from there onwards to Greenland and America. Norway was united under Harald Hårfagre (Fairhair), traditionally in 872. Many Norwegians chafed under central rule, taxes and men of the King taking to violent guesting (coming to farmsteads and forcing the locals to feed and house them for free) and opted to vote with their feet - they moved to Jämtland, Hälsingland, Härjedalen, Orkney, Faroe islands and Iceland.

The Norwegian Kings also attempted to acquire royal land to finance their rule. Combined with an increase in population during the medieval warm period there was a lack of land. This led to conflicts and some being willing to move to new places such as Iceland and Greenland.

Iceland and Greenland, with plentiful fishing and (at least for Iceland) plentiful grazing, wild fowl egg collection and lots of fish would at the time seem like a decent option to central and northern Norway, even southern Norway if a conflict or a lack of land prompted someone.

The nature of Norse justice also fed into this system. Conflicts, drunken brawls or old family feuds could brew over into murder. A murderer would be sentenced at the thing to become fredlös or "peaceless", which meant that anyone could harm him and take his things without reprecussions.

Naturally, men who faced such sentences would rather take what they could of their posessions and sail away to start over somewhere else with their household.