Mastodon’s summer is filled with reasons to celebrate.

Leviathan is a monument in metal; a sprawling epic woven with Herman Mellville’s spirit, Neurosis’ atmosphere and a rhythmic, percussive energy not often seen in metal. Their best album, it turns ten next month.

Their latest, Once More ‘Round the Sun, carries the torch one step further: A career-encompassing album that hurls some of the off kilter energy of Crack the Skye into The Hunter’s hyper-melodic framework. That it’s both their catchiest album yet and heaviest in years speaks volumes. Literally. In their 15 years together, Mastodon’s sound has been ever changing, continually evolving but always definitively their own. Through six albums they’ve reinterpreted and refined the Mastodon aesthetic to their own standards; what some fans might call a simplification of their sound they consider refined songwriting. Mastodon’s evolution is non-linear, and Once More ‘Round the Sun is the sum of its parts: Blood Mountain meets “Blood and Thunder,” with the scope of “Oblivion” tailored to the memorability of “Curl of the Burl.”

Most importantly, it’s referential without being regressive, a luxury earned from a decade-plus of wearing heavy metal’s gaudy crown.

But Mastodon have never rested on their laurels. In the ten years since Leviathan’s release they’ve carried on with kaleidoscopic progressive metal masterpieces that have woven personal storytelling and arena metal melodies into the fold.

We spoke with guitarist Bill Kelliher after the band’s brief delay with border patrol to see what makes Mastodon such an unstoppable force in metal.

AUX: You were saying you guys have calmed down a bit from that rockstar lifestyle…

Bill Kelliher: You have to.

AUX: You’re 14 years in as a band…

Almost 15.

And that’s not counting the bands you were in before. This far into your career, what defines you guys as a band?

That’s a good question.

Who is Mastodon now, in 2014?

I don’t know. At the moment, we’re a pretty steady fuckin’ rocking machine, I must say. Everybody’s been good on tour, not partying and not drinking. We’re playing like an hour and a half set every night, we’re whipping out seven or eight old songs we haven’t played in six years, two new songs, and a couple of the regular headbangers are in rotation. We’re a pretty well-oiled machine at the moment even though we’ve only been out for like 10 dates. It’s going really well. The tour is awesome, all of the other bands [Kvelertak, Gojira] are great, great people. It seems like a really good package for a kid who’s into metal and wants to see three great bands.

14 years, man… time flies. You’re pulling out the old stuff, too, and you’re in kind of an interesting position. Leviathan has its big 10th anniversary coming up, but you’ve also got a new album that comes out two months earlier. With the balance between old and new stuff, do you feel pressure to do these “legacy” set lists?

No, not really. We were trying to get together two years ago, it was the 10th anniversary of Remission, which came out in 2002. We have a Remission re-release coming out, with all new artwork, remixed, remastered, shit like that. We were going to come out and start playing the whole record. For me, some of those songs, it wouldn’t matter if we ever played them again. I liked them all at the time, they were great, and I know a lot of people will say ‘oh, it’s your best record!’

Well, I don’t think so. I love the record, I love all the songs. But that was a point in time where we toured and we played those fucking songs like every night for five years. We’ve played almost every song off Leviathan on tour before as well. For me, when I see a band I like to see a good mix of a lot of stuff, but I can see where it’s cool to play to the legacy of the album. For me, seeing the Melvins play all of Houdini or Stoner Witch, I mean that was fucking cool.

Mastodon feel very democratized, the way you guys write songs. It seems like you all have your own approach, and some guys take different leads on different songs. Is that just the way it happens naturally, or is that a concentrated effort?

It’s kind of the way it happens. Brent and I don’t ever really sit down long enough to write anything together, you know? It’s more like… he writes something and I play off it; I write something and he plays off it. Sometimes we might add stuff to each other’s songs here and there—rarely that happens, but when it does it’s great. We don’t force it, we don’t say “you and I have to sit down to write together.” That’s just not the way we work. I’ll come up with some riffs, or he will… “Chimes At Midnight,” that first riff was his, the second riff was his, and the third riff was mine.

Actually, the second and third riffs in that song, I was playing the vocal melody and he started playing another riff and I said ‘that would go with this, perfect,’ and we just started playing them back to back. Somehow the real slow beginning came in later on and it just kind of grew in the studio.

I feel really positive about the record. I don’t know how fans are going to feel about it…

I think they’re going to love it. I don’t know if it’s just something I’m noticing, but it feels a little faster, a little heavier, but it still has those hooks. Almost like a heavier take on The Hunter.

I can see that. But a lot of people didn’t like The Hunter. [With each album] I think we lose 10 per cent of our fans and then we gain, like, 80.

It’s better to be polarizing, anyways.

That’s exactly what it is. Every record that we do has a little bit of something different in it, you know? We’ve never set out to be like ‘hey, we’re only going to play this style of music, we’re only going to sound like this.’

There’s almost this perception that you guys are simplifying your sound, but there’s also always this lingering sense behind it all that you’re liable to go nuts at any moment

People might listen and say that we’re getting simplified, but to me it’s harder to write a rock record than it is to just go crazy and write sporadically.  To actually write a song like “Colony of Birchmen” or “Blood and Thunder,” those are simple, easy songs, but when we were writing them it wasn’t easy. It was like, ‘this is fucking hard, what’s going to come next? How are we going to make these simple four riffs work together in a way that’s not boring?’

The new one strikes me as very immediately catchy. Some of the hooks really grab you, but it still hits. The first half the record is really catchy and memorable without being uncompromising and then from there I feel like it gets a little more out there as it goes on. Is that a sequencing thing? Is that something you look at when you’re recording? I know you recorded more songs that aren’t on the album.

We have a couple more songs that might make it to a winter release.

Softer… they were more Brents songs, really soft. They didn’t seem like they fit on the record. The record, to us, was… these first 12 or 11 songs feel like a really fast moving rock record. Like for the summer release—Let’s get people fucking moving at the festivals. Let’s play these new songs. That’s kind of how we looked at it.

Plus we really had to cut some songs out. We had too many.

You don’t want to have a 75-minute record.

We don’t. There’s no point. A, after 55 minutes I’d just get bored of listening to the same record by the same band. And B, the record company only pays you for a certain amount of songs. You’ve got to choose your decisions wisely when it comes to the record industry.

Do you have a favourite thing about the record? There’s a lot of weird flourishes on there, some steel guitar, the Coathangers doing their thing on “Aunt Lisa.” Is there something that stands out to you?

Every song has its own special moment for me. The opening of the record, I got to play my acoustic guitar, which was awesome. Lots of 12-string guitars in there. All of the solo work in “High Road,” I did that because that was my song. All the harmonies… there’s a lot of special moments for me.

So, touring. You’re probably out for a while with this one?

This tour is only another, like, five shows… then the album comes out. We’ve got three European tours to do this summer, a couple festivals… one in Canada, in Montreal. We’re doing festivals in the States, and then when the festivals are over with, when it’s time to do something like this again, I think we’re going to take this same line-up back out again and hit all the cities that we didn’t hit this time around.

I feel like Kvelertak are one of those bands who are always in North America, even though they’re from Norway.

This looks a little like Oslo, out here by the water…

As someone who’s been listening to Mastodon since he was 15, it’s almost surreal to see all of these young kids out here waiting by the water for the show hours before doors open. It’s a new generation of Mastodon fans.

That’s something I was thinking of the other night in Pittsburgh. There was this really little kid, probably no older than nine or 10 in the front row with his dad holding him right against the fence. I bring my kids to shows too. Maybe this is going to spawn a whole new group of fans? That would be really cool. Obviously it’s the younger fans you want to get. The older fans get picky, they don’t come out to the shows, they don’t spend the money. They just complain about it on the internet.

Speaking of the Internet, I’m curious about the packages you’re putting out for this album. The vinyl pre-order was huge.

Everyone’s complaining about that because it’s “too expensive,” it’s $70. There’s four huge lithographs in it! They’re $100 a piece. I know the minute they’re on eBay that’s how much they’re going to be.

It’s not the main pressing, is it?

It’s a special order. There will be a regular one. That one’s limited to like 3,000 or 5,000 or something. There are people that love vinyl. It’s made a huge comeback.

I’ve sometimes had some trouble finding your stuff on vinyl…

Dude, what are you talking about? Like in stores? All of our records are out there. Relapse keeps on pressing Call of the Mastodon in every colour you can imagine.

Is that something you get into, the coloured vinyl and special editions?

I’ve been asking Warner Brothers to do a fucking picture disc of The Hunter and Crack the Skye for ages. Or at least re-release them…

As a collector, that’d be great.

I have a big collection of records, but even I don’t have all of our records.