All that magma (well, most of it) that is erupting from the volcano is being fragmented into tiny glass shards that we call “ash” and all that ash is being shot into the air at astounding rates – for very large eruptions, it could be as high as 9,500 kg/s for a VEI 7 eruption. In the end, your average eruption is releasing millions to trillions cubic meters of ash into the atmosphere. 

Most of it falls near the volcano (within tens of km), but a significant portion can travel far away, drifting in the atmosphere for hundreds, thousands, tens of thousands of kilometers around the globe. That ash becomes the telltale signs of an eruption that may have much of its record erased by future eruptions or by the relentless powers of weathering, erosion and transport.

Volcanic ash is really just amix of shattered rock, minerals and glass. The shattered rocks are from the physical breaking of the pre-existing material like solidified lava in the conduit (accidental material), while glass is quickly quenched magma from the eruption (juvenile material). 

The minerals could come from either the accidental or juvenile material of the eruption. When you’re trying to identify a layer of volcanic ash, you can look at the shape of the glass shards, the mineralogy of the ash or the composition of the glass
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This is one of the wrinkles associated with using Gmail's otherwise awesome IMAP feature, which effectively turns your mail client into an extension of the mail server. (You can learn more about this in my old post, Use Gmail IMAP with Your Desktop E-Mail Client.) Unfortunately, Live Mail lacks any kind of setting for limiting the number of messages it downloads; with IMAP, it's all or nothing.

Fortunately, Gmail itself offers a way to close the spigot, so to speak. All it takes is a quick trip to the control panel:

1. Open your browser and connect to your Gmail account.

2. Click the little gear icon in the top-right corner, then click Mail settings.

3. Click the Forwarding and POP/IMAP tab, the scroll down to Folder Size Limits.

4. Enable this setting: Limit IMAP folders to contain no more than this many messages.

5. Choose a number of messages: 1,000, 2,000, 5,000, or 10,000. (My advice: start with 2,000 and see if that's not enough. You can always increase it later.)

fter all, Google's mail service lives in your Web browser, and when you can't get online, you can't access your messages (new or old). This is true of other Web-based mail services as well, like Hotmail and Yahoo, but Google recently unveiled a new option for offline mail access.

Known as Gmail Offline, this browser plug-in allows users to read, respond to, and search mail even when there's no Internet connection. It has a nice-looking, simplified interface that's similar to what you typically see in Gmail--but with fewer options.

Unfortunately, for the moment Gmail Offline is available only for Google Chrome. On the plus side, similar plug-ins are forthcoming for Google Calendar and Google Docs.

There is, of course, another option, one that can solve the offline problem for not just Gmail, but also Hotmail and Yahoo Mail Plus: an e-mail client like Windows Live Mail 2011 or Mozilla Thunderbird 6. Programs like these can be configured to download e-mail and store it locally, thus allowing you to read, respond, and search--just like with Gmail Offline. Just make sure you stick with a POP3 configuration rather than IMAP, as the latter requires a live Internet connection for many functions.