# What is the opposite of 'hollowing out' in this context?

I am having trouble finding a suitable word/phrase to describe the following situation:

If the middle of something is eroded away, it is hollowed out. What would be a suitable way to describe the creation of the same shape but through the sides growing upwards rather than the middle being hollowed out? Almost like two pillars growing on either side.

Another way that I visualise the same problem is to imagine a bar graph. If the middle bar stayed where it was but the two bars either side went up, what would be a good phrase to describe it?

Growth at the extremities?

• So you mean that something surrounds another thing? – NVZ Apr 16 '17 at 10:52
• To some degree, yes. Another way that I visualise the same problem is to imagine a bar graph. If the middle bar stayed where it was but the two bars either side went up, what would be a good phrase to describe it? Thank you for your reply – Tom Cadwallader Apr 16 '17 at 10:55
• Think of The Little Prince. There is the drawing of the boa digesting an elephant: it creates a bulge. The "opposite" of hollow out is to bulge. Think of a beer belly on a man. Similar to, with regard to a surface, concave (hollow out) and convex (bulge). – Lambie Apr 16 '17 at 11:54
• Assuming whatever variable was being charted had anything like a normal distribution / bell curve, any "hollowing out" of the central bars would represent increasing polarization. – FumbleFingers Apr 16 '17 at 12:28
• You lost me at bar graph. – lux Apr 16 '17 at 20:23

Accreting would be the opposite of hollowing out:

Growth or increase by the gradual accumulation of additional layers or matter.

‘the accretion of sediments in coastal mangroves’

Enclosing would be what you describe as a build up around a void:

Surround or close off on all sides.

‘the entire estate was enclosed with walls’

"Peripheral growth" could work depending on context.

Definition of 'peripheral': Relating to or situated on the edge or periphery of something. https://en.oxforddictionaries.com/definition/peripheral

Definition of 'periphery': The outer limits or edge of an area or object. https://en.oxforddictionaries.com/definition/periphery

If you want a high-register term, try immure.

1a : to enclose within or as if within walls
b : imprison
2: to build into a wall; especially : to entomb in a wall

[...] "Immure," which first appeared in English in the late 16th century, literally means "to wall in" or "to enclose with a wall," but it has extended meanings as well. In addition to senses meaning "imprison" and "entomb," the word sometimes has broader applications, essentially meaning "to shut in" or "to confine." One might remark, for example, that a very studious acquaintance spends most of her time "immured in the library" or that a withdrawn teenager "immures himself in his bedroom every night."

"Immure." Merriam-Webster.com. Merriam-Webster, n.d. Web. 16 Apr. 2017.

but realistically, wall, as a verb, will do the job.