Is it normal for the graphics card to reach 80 degrees?
Did your card reach that 80C? Under what load? That game? Mafia?
Under heavy load (gaming or otherwise) and depending on the card, its cooler (how big a sink how many fans), the heat generated by other parts like CPU and how it's handles (CPUs cooler), general air flow/ventilation in the case (how many fans, directions and where in the case) yes it can reach those temps. Nothing specially alarming, unless it gets there very quickly and under a load which would not make it run that hot normally.
I have a GTX 1070 and in all the times I checked how hot it got during operation I don't think it has gone higher than 74-75C. But that's because of all the reasons I said above. My case with its ventilation and the card with its cooler and the certain load its max temp was that. Same conditions with a different load (for example a game that would keep the GPU in my system around 90-100% load for more clock cycles - longer time) it might have gone higher.
Decent cards (don't know your 1070's brand model) have good cooling. So depending on the load if it didn't have that good cooling it might even go higher under same load. Also they have controllers and if the heat would get to a point where it's dangerous for card operation and health it should clock down to make it less hot.
All that said it's always better to try improve air flow/ventilation inside the case. It won't make the card like 10C cooler under same load that gets it to 80C but it's better for all components.