Ground wire to negative battery post got so hot it melted battery post. Why?

[adorenedeet]

Was going to mow yard and after filling fuel checking oil and such I attempted to start my mower which it did after about 10 seconds. Put it in reverse and it died almost immediately. So I then tried to start it again. Didn't start and almost sounded like battery was low (new battery this year). I tried to start again then noticed smoke coming from between my legs. Craftsman LT1000 battery under the seat. The black wire going the the negative post had gotten so hot it melted the post down to where the bolt didn't go through the hole in post...it was just resting on top of melted post. What would cause this to happen?

 

[bertsmobile1]

The terminal became loose and sparked.
Sparks raise the temperature so the resistance increases so it sparks more & gets hot enough to melt the lead ( ~ 700 deg )
You can buy a lot of arc welding sets that will weld steel which run off a car battery.
SO you might get by with cleaning the battery & wire really well then drilling a new hole or filing to old one enough to get purchase with a nut bolt and some washers.
Clean the other end of the cable and the bolt where it grounds .
When all done up tight paint it over with liquid electrical tape.
This will both stop the bolts working loose and corrosion forming.

 

[adorenedeet]

The terminal became loose and sparked.
Sparks raise the temperature so the resistance increases so it sparks more & gets hot enough to melt the lead ( ~ 700 deg )
You can buy a lot of arc welding sets that will weld steel which run off a car battery.
SO you might get by with cleaning the battery & wire really well then drilling a new hole or filing to old one enough to get purchase with a nut bolt and some washers.
Clean the other end of the cable and the bolt where it grounds .
When all done up tight paint it over with liquid electrical tape.
This will both stop the bolts working loose and corrosion forming.

Thank you Bertsmobile1! I will do this and cross my fingers!