When it comes to information about the world's volcanoes and their relative positions on the earth, I'm sorry to say my notebook couldn't be more MTE. On the other hand, I do know a lot about TI[MTE]BOW, so I was still able to solve the puzzle, albeit at a rather sedate pace and with one error. I guessed wrong at the cross between Norfolk Southern and others: Abbr. (44D) and46A "Bandstand Boogie" bandleader Larry (ELGART). I guessed RtS for 44D, but with a little more thinking after the "Almost there" message, I realized RRS was wanted.
The theme charms and amuses me. I love it that the name of MTEREBUS has the word rebus right in it. What could be more apt for a rebus puzzle? Apt!
Of the theme answers, the clue for FORTSU[MTE]R was my favorite (Site of a famous opening shot). And, although not one of my personal strengths, I liked the clue (Not remain aloof) and answer (MIX) at 35D.
The clue that surprised me the most today was "Courageous and energetic sort, they say" (ARIES). I don't know that I've ever seen a clue based on alleged characteristics of an astrological sign before. I would never have gotten it without crosses. I'm guessing Horace enjoyed it. And possibly 39A (TIS) as well.
I didn't enjoy the clue for 1A at all (Doesn't lose) and the answer is no prize either (HAS). It's fine, but it's certainly not fine. I also thought the cluing Smell like for REEKOF at 49D was a little off.