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What is Accretion?

Mary McMahon
Updated May 21, 2024
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Accretion is a term used to refer to a situation in which something is growing in size. The term appears in a number of different contexts, from finances to astrophysics. Accretion process are constantly ongoing in a variety of locations around the Earth and the universe. Since most of the settings in which this term is used are in the sciences, this article focuses on accretion in areas like astrophysics, meteorology, and geology.

In the sciences, this process occurs as smaller pieces of material stick to larger pieces of material, gradually allowing the larger piece to grow in size. One example of this type of accretion occurs at some tectonic plate boundaries, as material is transferred from one plate to another. Another occurs with landmasses which grow as a result of the deposition of sediment. Islands, for example, can grow as sediment is deposited on one shore, and beaches often experience accretion during stormy weather as sediment is moved and redeposited.

In the atmosphere, accretion can be involved in some weather processes. For example, hail forms as small seedling ice crystals grow larger as a result of accretion. The crystals attract other crystals, slowly growing until they precipitate out of the clouds and hit the Earth. It is also possible for ice to form around particles of dust and other materials, in another example of an accretion process.

Accretion also occurs in space. Many celestial bodies have attained their size as a result of this process, with gravity in the early stages of their formation attracting particles and other materials from the surrounding area to allow the object to grow. In binary star systems, a phenomenon called an accretion disk is often seen, with a denser star pulling material off another star, causing a halo of material to settle around the denser star. If the conditions are right, the material will be attracted to the surface of the denser star to fuse with it, making it larger.

All of these processes allow objects to grow and shrink in size by moving smaller materials around. The Earth and the universe itself are subject to a number of dynamic processes which ensure that few things remain the same for very long. These processes are involved in everything from the formation of new stars to stormy weather on Earth, constantly repurposing materials which have been used in a variety of ways throughout the history of the universe.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By nony — On Jul 12, 2011

I watched a television show once about how the moon was made. One of the theories put forth was that the moon was actually made up of material from the Earth, which was hurled into space after an asteroid impact.

Through an accretive process over millions of years, the moon gathered more and more space stuff and debris until it become what we know as the moon today.

I think that the theory makes sense because I’ve also viewed the moon as a cousin of Earth, not something as alien as we have thought it to be.

By hamje32 — On Jul 12, 2011

@Charred - Foul weather can be rough indeed, but I think the worst example of something growing in size is long term debt – because it never ceases to increase.

The United States has piled up trillions of dollars in debt over the course of many decades, and I just hope that politicians have the political will and backbone to turn things around.

There are some glimmers of hope on the horizon, but there is resistance as well, because a lot of the debt came through entitlements. I certainly don’t want to see needed entitlements be cut, but I’d just like the government to curb its spending so that the United States doesn’t default like some other nations have.

By Charred — On Jul 11, 2011

We live in the Midwest, and during tornado season, I guess you could say that we get plenty of accretion.

We get these very strong thunderstorms with hail that is sometimes the size of golf balls. One year in particular the hail damage was devastating. It damaged my car and my roof to boot.

Just about everyone in our neighborhood (myself included) had to get a new roof. Fortunately the insurance covered it, which was good because there was no way I could have afforded a new roof on my own.

But to sum up, if you want to see accretion power in action, come visit Oklahoma and tornado alley some time. Just keep your car in the garage while you’re here.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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