Perhaps they're worried their readers won't be able to keep up and they think let's get all the world building done in one clump? Maybe fantasy writers are inherently worrisome? After all, most genres allow the story to unfold and trust their readers to figure it out as they read along. Who really knows?
It's easy to spot the obvious info dump--just look for pages of technical or world-building information that goes on and on... leaving the reader feeling, well, like they've just attended a lecture delivered by a bored, monotone profession on a Friday afternoon on the last day before school break...
Well, you get the idea. But if you don't, here are two examples:
"Gee, Jane, did you know the baddies are from Planet X, have three eyes, have ten stomachs and eat humans, live for two hundred years and can fly?"
"No, John, I didn't."
"Yup. The planet was destroyed in a civil war that lasted three hundred years. The Zargonots pledged to overthrow the vicious Scallawags and developed a cyber weapon that wiped out all electronic devices. After they won, the Zargonots tried to rebuild their infrastructure but without the Scallawags help, they couldn't. When they ran out of food, they sent a probe into space, hoping to find a new planet--one that they could take over. The probe veered off course and discovered our lovely blue orb, and now they're here!"
Gasps. "You're kidding. Tell me more!"
Okay, so this may be obtuse, and perhaps you're chuckling (you should be, btw), but I've actually read this form of dialogue in published books. When an author conveys info via dialogue, it can come off as stilted and unbelievable. Who wants to be lectured? Just ask my teen, it's annoying!
Another form of info dump comes from the protagonist in an internal dialogue.
Jane grasped the gun in her hand, aiming low to hit the slobbering beast stalking her. This was the first time she'd seen a space alien and she'd never imagined anything quite so disgusting. Planet X grew fierce some creatures with an appetite for humans. Their three hundred year war had decimated their food population and now they had set their sights on Earth...
Did you catch it? The dump?
Also hidden within this last example is something I like to call a narrator tell. Really, how would Jane know so much about Planet X if she's never been there? Who told her about the war? The narrator may know it, but how would Jane? (more on this in an upcoming post).
But don't get me wrong. Info dumps have their place. Yes! In first drafts! Those dumps are often full of plot points and character development. Once you have a draft, go back and pull that information apart. Keep some, inserting it judiciously throughout the story (with it being revealed by multiple characters.) The rest, save in a separate file, and never let it see the light of day.
Just remember, even though you may love all this detail, your reader may not. And it's never wise to bore your reader.
I wish you happy writing!