Historians have a difficult task, if not all facts have been discovered yet, with doing what? not publish the findings until all evidence and facts are discovered. make up missing pieces of information depending on the bias of the writer. attempt to re-create a historic event to find what probably happened. write only the true evidence from as many perspectives as possible.

Historians should have an impartial viewpoint and use as many details as possible while describing an Historic event, this is hard to achieve especially when there is not enough information (like documents, pictures, reports, etc.) that they can use to reconstruct the order of events. That's why they Attempt to re-create a historic event to find what probably happened. However, these are only hypothesis and new discoveries can prove if they are wrong or right.  

this forms a narrow, steep sided inlet (sometimes deeper than 1300 metres) connected to the sea. the terminal moraine pushed down the valley by the glacier is left underwater at the fjord’s entrance, causing the water at the neck of the fjord to be shallower than the main body of the fjord behind it.