Weight gain from XC?

Hi,

At the end of November when I put my bike in the garage for the winter
I weighed 93kg. I have been skiing about 8-12 hours per week (50/50
classic-skate) and which is at least 3-4 hours more on average than I
did on the bike. I also think my skiing is more intense than the bike
riding was (at least during the fall). I haven't changed my diet in any
way. My weight is now 103kg. I notice that certain parts of my quads
are much larger now, and my triceps too, and I suspect other places
too. Fat is hard to judge, but I think it is pretty constant.

Is it common for skiing to encourage the development of bulk muscles? I
for some reason always assumed it would be slimming like running. I
certainly didn't expect to gain 10kg in 3 months! It dosen't bother me,
I am just curious about the development.

Joseph