Around 1 a.m. yesterday, a dam burst near Harriman, TN. This wasn't just any dam: it held back millions of cubic yards of sodden fly ash -- the toxic byproduct of coal burning at the Tennesee Valley Authority's Kingston Steam Plant. The gray sludge soon buried about 400 acres six feet deep. One house was ripped from its foundations, and several others were damaged and evacuated.

There were no fatalities. However, the long-term environmental damage to the immediate area, the surrounding ecosystem, and to a crucial watershed that supplies drinking water to millions of people are likely to be severe.

The Knoxville News-Sentinel is offering extensive ongoing reporting of this disaster -- as is the Nashville Tennessean, WVLT volunteer TV, WFPL-FM in Ky., and other local news organizations.

How bad is this? Wendy Redal, guest blogging for the University of Colorado's Center for Environmental Journalism, wrote: "According to the Environmental Protection Agency, the spill released 2.6 million cubic yards of slurry, enough to fill almost 798 Olympic-size swimming pools. The TVA spill [is] nearly 50 times bigger than the Exxon Valdez spill in Alaska in 1989."

(Note: Since Redal's post was published, the Knoxville News-Sentinel tweeted: "Updated estimate from TVA to EPA for spill is now 3.1 million cubic feet of fly ash & water vs 2.6 million cubic yards earlier." I'm checking on the change of units.)

CEJ director Tom Yulsman added to Redal's post: "If you haven't heard about the events she describes here, you're probably not alone. I found no mention of the catastrophe on the Web sites of the New York Times, CNN or Fox News, and a Google News search only turned up stories by local Tennessee media." (Note: Yulsman is updating this post with more background, news, and context)

I've just done a similar search of Google News, Yahoo News, and the sites Yulsman named, and I found the same lack of national coverage -- although there was a brief AP story.

This might not be surprising from CNN, which earlier this month cut its entire science, environment, and technology news team. Not surprisingly, the Society of Environmental Journalists and several other journalism organizations have formally protested the CNN cuts.

Of course, CNN Center in Atlanta is only about 200 miles from Harriman, TN -- just a three-hour drive... They could have thrown a regional news team on the story, but... On the bright side, the Knight Science Journalism Tracker notes today that the NY Times is forming a new reporting unit for environment and climate change coverage. So hopefully they won't keep overlooking stories like this.

The lack of national mainstream news coverage of this disaster isn't stopping the story from spreading. Tenn.-area news orgs and individuals from all over the US have been tweeting about this story, and many people have been blogging it. There are also videos on YouTube. Twitter is an easy way to find this coverage. Just search there for the hashtag #coalash, as well as for the terms coal ash and TVA.

When I first learned of this disaster from SEJ colleagues by e-mail this morning, I immediately launched the Twitter hashtag #coalash. Off and on today I've been posting links to news, context, background, opinion, resources, maps, and multimedia related to this unfolding story. Even EPA's Web manager, Jeffrey Levine, was tweeting relevant EPA maps and facility info.

Other Twitter users, including several Tenn.-area news orgs, adopted the hashtag. This made it easier for people to find and follow their coverage. Using a hashtag provides a broader view that includes local news coverage and extends beyond it. At the same time, a hashtag can amplify the reach of local stories. Online, this reach becomes especially crucial in the absence of delayed or absent mainstream national news coverage.

So the lesson is: When big news breaks in your community, start tweeting it with a hashtag. If no one has launched a hashtag, pick one. (Here are some tips for choosing and launching hashtags. It's about event hashtags, but applies to breaking stories too.) If a hashtag is already in play, use it -- consistently. It's an easy aggregation tool that makes stories findable, and puts them on more people's radar.

Also, encourage people to retweet you posts and include the hashtag. On Twitter, every reader is a potential megaphone, with the possibility to grow your online audience, strengthen your brand, and hasten the spread of important news.

...But don't depend that everyone will understand or use your hashtag. Keep a browser tab or two open showing Twitter searches for other common terms being used for your story on Twitter. Retweet (using the hashtag) key items that originally were posted without the hashtag. This spreads awareness of the hastag and publicly recognizes people for covering or amplifying the story.

And of course, if misinformation or rumors erupt, tweeting with the hashtag can be an effective way to counteract those problems fast.