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Home » Rocks » Igneous Rocks » Basalt

Hot Spots Hot Spots A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity. Hot spots can also develop beneath continents. The Yellowstone hot spot, for example, has produced a series of volcanic features that extend in a northeastern direction. The features stretch from the U.S. States of Idaho and Oregon, some 650 kilometers (400 miles) to northwest Wyoming. Images should be taken against a solid background. Images should have neutral backdrops to keep the focus on the item. Images should be evenly lighted so the image shows as many details as possible. Do not scale up image sizes and do not add thumbnails to your images because these practices can affect the clarity of your images when presented.

Basalt: A fine-grained igneous rock that is usually black in color. The specimen shown is about two inches (five centimeters) across.

What is Basalt?

Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. It has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.

Olympus Mons Volcano: This shield volcano is composed of basalt and has enormous calderas at the summit. Olympus Mons is the highest topographic feature on Mars and is the largest known volcano in our solar system. It is about 375 miles (600 kilometers) in diameter and 15 miles (25 kilometers) high. NASA Mars Orbiter Camera image.

Earth's Most Abundant Bedrock

Basalt underlies more of Earth's surface than any other rock type. Most areas within Earth's ocean basins are underlain by basalt. Although basalt is much less common on continents, lava flows and flood basalts underlie several percent of Earth's land surface. Basalt is a very important rock.

Basalt on Moon and Mars

Basalt is also an abundant rock on the Moon. Much of the Moon's surface is underlain by basaltic lava flows and flood basalts. These areas of the Moon are known as 'lunar maria.' Large areas of the Moon have been resurfaced by extensive basalt flows which may have been triggered by major impact events. The ages of lunar maria can be estimated by observing the density of impact craters on their surface. Younger basalt flows will have fewer craters.

Olympus Mons is a shield volcano on Mars. It, like most other volcanic features on Mars, was formed from basaltic lava flows. It is the highest mountain on Mars and is the largest known volcano in our solar system.

Basalt-Forming Environments: This map shows the location of oceanic divergent boundaries and hotspots. These are locations where large volumes of basalt have been formed. Map copyright by Geology.com and MapResources. Locations generalized after United States Geological Survey, Geologic Investigations Map I-2800: This Dynamic Planet.

Igneous rock composition chart: This chart shows that basalt is typically composed of pyroxenes, plagioclase, micas, and amphiboles.

Basalt-Forming Environments

Most of the basalt found on Earth was produced in just three rock-forming environments: 1) oceanic divergent boundaries, 2) oceanic hotspots, and 3) mantle plumes and hotspots beneath continents. The images on this page feature some of these basalt-forming environments.

Sea floor pillow basalts on the Juan de Fuca Ridge, a divergent plate boundary located about 150 miles (240 kilometers) west of the Washington-Oregon coast. This lava flow, produced by a fissure eruption, was about five years old when the photograph was taken. NOAA Ocean Explorer image.

Hawaii Basalt Flows: Lava flows dump into the Pacific Ocean on the coast of Hawaii. Multiple locations where hot lava streams into the ocean can be seen in this image along with a red-hot lava flow traversing the lava field. This photo shows the enormous extent of the flows. They extend from the shoreline up to the horizon. A volcanic plume from the Pu`u `O`o vent can be seen over the horizon near the center of the image. The lava in these flows originated from the Pu`u `O`o vent. USGS image.

Basalts at Oceanic Divergent Boundaries

Most of Earth's basalt is produced at divergent plate boundaries on the mid-ocean ridge system (see map). Here convection currents deliver hot rock from deep in the mantle. This hot rock melts as the divergent boundary pulls apart, and the molten rock erupts onto the sea floor. These submarine fissure eruptions often produce pillow basalts as shown in the image on this page.

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The active mid-ocean ridges host repeated fissure eruptions. Most of this activity is unnoticed because these boundaries are under great depths of water. At these deep locations, any steam, ash, or gas produced is absorbed by the water column and does not reach the surface. Earthquake activity is the only signal to humans that many of these deep ocean ridge eruptions provide. However, Iceland is a location where a mid-ocean ridge has been lifted above sea level. There, people can directly observe this volcanic activity.

Thermal image of a hot basalt flow on the flank of Hawaii's Kilauea volcano. Hot lava at the front of the flow is revealed in yellow, orange and red colors. The channel that it flowed through on the previous day appears as a purple and blue track. United States Geological Survey image.

Oceanic Hotspots

Another location where significant amounts of basalt are produced is above oceanic hotspots. These are locations (see map above) where a small plume of hot rock rises up through the mantle from a hotspot on Earth's core. The Hawaiian Islands are an example of where basaltic volcanoes have been built above an oceanic hotspot.

Basalt production at these locations begins with an eruption on the ocean floor. If the hotspot is sustained, repeated eruptions can build the volcanic cone larger and larger until it becomes high enough to become an island. All of the islands in the Hawaiian Island chain were built up from basalt eruptions on the sea floor.

The island that we know today as 'Hawaii' is thought to be between 300,000 and 600,000 years old. It began as an eruption on the floor of the Pacific Ocean. The volcanic cone grew as recurrent eruptions built up layer after layer of basalt flows. About 100,000 years ago it is thought to have grown tall enough to emerge from the ocean as an island.

Today it consists of five overlapping volcanoes. Kilauea is the most active of these volcanoes. It has been in amost continuous eruption since January, 1983. Basalt flows from Kilauea have extruded over one cubic mile of lava, which currently covers about 48 square miles of land. These flows have travelled over seven miles to reach the ocean, covering highways, homes and entire subdivisions that were in their path.

Columbia River Flood Basalts: The Columbia River Flood Basalts are an extensive sequence of stacked lava flows that reach a cumulative thickness of up to 6000 feet. The outcrops in the foreground and in the distance of this photo are all made up of layered basalt flows. Although basalt is typically a dark black rock, it often weathers to a yellow-brown color similar to the rocks shown here. Public domain image by Williamborg.

Columbia River Flood Basalts Map: A map of the area underlain by the Columbia River Flood Basalts in Washington, Oregon, and Idaho. The area shown is what has not yet been eroded away - the original extent of these basalt flows was much greater. Over 300 individual flows have been identified, and several hundred meters of basalt underlies much of the area shown in the map above. Map copyright by Geology.com and MapResources.com.

Plumes & Hotspots Below Continents

The third basalt-forming environment is a continental environment where a mantle plume or hotspot delivers enormous amounts of basaltic lava through the continental crust and up to Earth's surface. These eruptions can be from either vents or fissures. They have produced the largest basalt flows on the continents. The eruptions can occur repeatedly over millions of years, producing layer after layer of basalt stacked in a vertical sequence (see outcrop photo).

The Columbia River Flood Basalts in Washington, Oregon, and Idaho are an example of extensive flood basalts on land (see map below). Other examples include the Emeishan Traps of China, the Deccan Traps of India, the Keweenawan Lavas of the Lake Superior region, the Etendeka Basalts of Namibia, the Karroo Basalts of South Africa, and the Siberian Traps of Russia. (The word 'traps' is derived from the Swedish word for 'stairs,' which describes the outcrop profile of these layered basalt deposits, as shown in the outcrop photo.)

Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials. The best way to learn about rocks is to have specimens available for testing and examination.

The Roman theatre: (left) in Bosra, Syria. The dark building stone is basalt. Image copyright iStockphoto / Steve Estvanik.
Basalt paving stones: (right) on a city street in Rome, Italy. Basalt pavers were often used in areas close to volcanoes. Image copyright iStockphoto / Giovanni Rinaldi.

Uses of Basalt

Basalt is used for a wide variety of purposes. It is most commonly crushed for use as an aggregate in construction projects. Crushed basalt is used for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, filter stone in drain fields, and may other purposes. Basalt is also cut into dimension stone. Thin slabs of basalt are cut and sometimes polished for use as floor tiles, building veneer, monuments, and other stone objects.

At Google, gadgets are HTML and JavaScript applications that can be embedded in web pages and other apps, including Sites. These gadgets offer the ability to include external and dynamic content within your site, such as miniature applications and database-driven lists, incorporated with text and images for a seamless user experience.

Every Sites page is a potential gadget container. What's more, Sites offers a Data API that may be used in conjunction with gadgets to create powerful applications. That means as a gadget developer you can leverage the Sites API to build engaging tools for other Web developers and their audiences, as well for your own use.

When you build a gadget for Sites, it becomes available to millions of activeusers. Just submit your gadget to us, and it will appear where users can easily browse, configure, and add your gadget to theirSites.

So now you know Sites is a great distribution platform for your gadget, what areyou waiting for? Get started building gadgets for Sites now!

Sites gadget overview

Generically, gadgets are small utilities that generate or pull external information into web pages. In its simplest form, a gadget is a small .xml file that retrieves information with the ability to make it available in multiple web pages at once. In Sites, including a gadget results in an iframe that acts as the conduit for this external information. Some gadgets are no more than that, iframes that pass through information from another web site.

More advanced gadgets collect dynamic content and provide for interactive applications within your Sites pages. See Example gadget.

Gadgets consist of the following components:

• Gadget spec file - A .xml file that wraps HTML and JavaScript functions.
  
• Container page - The Web page where the gadget is inserted, in this case a Google Site.
  
• External data source - This is optional and may reside in the same location as the .xml file but is often called by the gadget spec over HTTP to provide its results.

Gadgets built for Sites may be used by all viewers of a site. They tend to be interactive, focused on pulling in dynamic content rather than on presentation, and are designed to complement the content of the site.

A calendar gadget is a good example of this distinction. A personalized calendar gadget in would likely show the calendar of the logged in user by default, while a calendar gadget in Sites might allow collaborators to select from a variety of location-specific calendars.

Sites gadgets allow you to present multiple pieces of information from external sources (say live diagrams from distinct but related performance dashboards) in a single page along with explanatory text published directly in Sites. This saves visual real estate while collecting disparate information on the same topic in the same view. Gadgets also allow you to include dynamic content that would otherwise be prevented by Sites security checks.

Warning: Gadgets built with the legacy gadgets API may work in Sites but are not officially supported. Built-in and feed-based gadgets are similarly not supported. Therefore, Google recommends you build all Sites gadgets using the current gadgets.* API. See this post for an explanation:
http://igoogledeveloper.blogspot.com/2009/09/more-things-change-more-they-stay-same.html

Example gadget

Here is a simple but popular Include gadget that does little more than provide an iframe for passing through other web content:

See Getting Started: gadgets.* API for a complete description of gadget tags and expected contents.

Hosting your gadget

Regardless of what your gadget does, its files must reside on the World Wide Web to be found and used. Any online location accessible over HTTP without authentication will do. Just remember, your gadget will have to be published in a public directory to be selected. Otherwise, users must embed it by directly inserting its URL.

Here are your gadget hosting options:

• App Engine - Capable of storing all files required by your gadgets. Does require some setup, namely the creation of projects and subsequent file uploads. But it will readily scale to a large number of users. You can create an application to store all of your gadgets and another to serve static files, including an app.yaml file resembling:

  If you put all of the gadget files in the static directory, you may then edit the files on your local directory and deploy to App Engine each time you make changes. If you have a file /static/gadget.xml, its URL will be: http://<your-app-name>.appspot.com/static/gadget.xml

• Any online location of your choosing - Completely under your control but also your complete responsibility. Downtime on your server may result in an outage for users of your gadgets.

Building your gadget

Gadgets are just HTML and (optionally) JavaScript, Flash or Silverlight wrapped in XML. The Gadget Developer Guide provides all necessary details for building your own gadgets. In addition, OpenSocial templates may be used to quickly build social applications in gadgets.

Here are the high-level steps for building a gadget for Sites:

1. Decide where your gadget will be hosted. See the Hosting your gadget section for descriptions of your options.
2. Create a new .xml file that will act as your spec using the text editor of your choice.
3. Decide on the content type, either HTML or URL, and specify it within the gadget .xml file, like so:
   <Content type='html'>
   This will almost invariably be HTML, which assumes all content is provided directly in the .xml file. But if you intend to supply the content in a separate file, use the URL content type. See Choosing a Content Type for a full description of their differences.
4. Create content in the gadget .xml file or in separate files called by the spec. See the Viewing example gadgets section for ways to examine existing gadgets.
5. Define basic preferences for the gadget that can be altered by users. See Defining User Preferences for instructions. To provide more advanced configuration, see the Allowing advanced user configuration section.
6. Define module preferences that only the gadget author may change. See Defining Gadget Preferences for additional details.
7. Test the gadget. See the Testing your gadget section for instructions.

Embedding your gadget

Gadgets can be embedded in Sites pages either by selecting it from the Sites gadget directory (which is synchronized with the iGoogle gadget directory) or by including its URL directly.

To embed a gadget in Sites:

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1. Go to the Sites page that will contain the new gadget.
2. Open the page for editing.
3. Select Insert > More gadgets.
4. Search for the gadget, select it from the categories on the left, or click Add gadget by URL and paste in the URL to your .xml file. Then click Add.
   Tip: This same Add gadget by URL method may be used to embed gadgets from iGoogle and anywhere else online.
5. Specify the gadget's dimensions, select from available settings and click OK. The gadget is added to your page.
6. Save the page to view and test your gadget in the site.

Testing your gadget

After building your gadget, you should test it thoroughly before using it and allowing others to do the same. Test your gadget manually by creating one or more test Google Sites and embedding your gadget. See the Embedding your gadget section for precise steps. The functionality and appearance of your gadget depends on the site that contains it. Therefore, the best way to debug your gadget is to test it in the context of an actual Google Site. Try switching between various Sites themes to ensure your gadget appears correctly in each.

As you test your gadget, you'll inevitably discover bugs and need to make corrections to your gadget .xml file. You should disable gadget caching while you're tweaking the XML. Otherwise, your changes won't show up on the page. Gadget specs are cached unless you tell Sites not to. To bypass the cache during development, add this to the end of the Sites page URL containing the gadget (and not the URL of the gadget spec .xml file):

Sites provides a standard UI for adding and configuring gadgets. When you add a gadget, it will display a preview and show any UserPref parameters that can be configured. Test updating various configuration values and adding your gadget to your test site. Confirm your gadget works as expected on the site itself. You should test that any UserPref you've defined can correctly be configured by the site administrator.

Then refer to the Preparing for Publication section of Publishing Your Gadget for other tests to carry out.

Allowing advanced user configuration

All gadgets may offer the ability to set basic user preferences, done through the UserPref section of the gadget spec file. These typically affect dimensions, scrollbars, borders, titles and gadget-specific settings, as depicted in the screenshot here:

But there are many cases where gadgets benefit from more advanced preferences than the standard UserPref components offer. Preferences often need to include features like custom business logic, validations, or pickers. The interface generated from the gadget UserPref sections supports a limited number of datatypes (string, enum, etc.), so validation of inputs like URLs or dates cannot be conducted.

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Further, in containers like iGoogle where the viewer and editor are the same, gadget authors can extended configuration as part of the standard view. In Sites, the viewer is not always the editor, so the gadget author can't guarantee the viewing user has access to update preferences. Social containers such as Sites cannot allow any user to modify the preferences, only the author.

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In Sites, the basic gadget preferences interface generated by UserPref can be replaced by a configuration view where many additional preferences and data types may be supplied, as in the screenshot shown here:

The configuration view is shown in place of UserPref settings at insertion time or edit time and allows you to set user preferences with a custom interface. And you can have custom input elements, such as for picking a position on a map rather than entering map coordinates.

Developers can use the standard setprefs APIs to save preferences in this view. See Gadgets XML Reference and the Saving State section of Developer Fundamentals for additional details. These views allow the container application to provide supplementary configuration information and are established in the gadget .xml spec files following the UserPref sections with an opening tag resembling:

For instance, the news.xml gadget that provides the configuration view above contains this section:

You can find this example and other Sites-specific gadgets with configuration views here:
https://www.gstatic.com/sites-gadgets/news/news.xml
http://gadgets.pardonmyzinger.org/static/qrcode.xml
https://www.gstatic.com/sites-gadgets/news/youtube_news.xml

Following best practices for Sites gadgets

Sites users want to look good on the web. Follow these best practices so your gadget blends seamlessly with the many themes used in Sites. See Gadgets Overview for details on creating gadgets. The rest of this section presents guidelines particular to Sites gadgets.

• Do not put sensitive information in gadget specs or titles because your gadget is viewable by the public. For example, don't include internal project names.
• To minimize visibility to your gadget, do not submit it to the iGoogle gadget directory or any other public listing service. Instead, have all users include it by URL only. In addition, you may create a URL-type gadget (rather than the typical HTML type containing all contents) that merely calls another file for its contents. With this pass-through option, only the URL of the second file is exposed. See the Choosing a Content Type section of Developer Fundamentals for differences between HTML and URL gadgets and the Gadgets are Public section of Writing Your Own Gadgets for other ways to mask your gadget.
• Most importantly, test your gadget on a number of different sites. Modify the site's background color, text color, and font face to ensure your gadget blends with a wide range of templates.