by George Weberhttp://www.andaman.org/BOOK/originals/Weber-Toba/ch2_today/textr2.htm
Toba Volcano: 2. The Sleeping Giant
Where the cataclysmic events of 73,000 years ago took place, there is now an idyllic landscape with a picturesque lake at its centre. The area has great beauty, friendly locals and many potential tourist attractions. Only the occasional slight tremor, or puff of smoke and a few hot springs give a tiny hint of the violence that is lurking below. In fact,
Toba is likely to have been the place where modern Homo sapiens most dangerous and fiercest struggle for survival began. Countless other species faced the same trial - and many did not make it. Our ancestors did.
Fig. 2-1. Today's topography around Lake Toba, the site of the last major Toba eruption 73,000 years ago.
Fig. 2-2. The eruption of 73,000 years ago left the Sibandung caldera. Lake Toba is surrounded by two small, active volcanos as well as several updomed areas and hot springs. These features indicate that there is activity below the surface today and that pressure is rising. Samosir island, too, is evidence for upthrust from below. From the record it seems that Toba produces major eruptions every 300-400,000 years and that it will erupt again - but not any time soon.
Volcanic features in and around Lake Toba today:
grey area Present-day topographic depression
green area Updomed areas
1 Sibandung caldera: made 73,000 years ago by the Toba YTT event (Young Toba Ash)
2 Haranggaol caldera: made 500,000 years ago by the Toba MTT event (Middle Toba Ash)
3 Sibandung caldera: made 800,000 years ago by the Toba OTT event (Old Toba Ash)
The MTT and OTT events were not as large as the YTT event of 73,000 years ago
but were still major eruptions of at least VEI 7.
V1 Tandukbenua (Sipisopiso) - young dacit-andesite volcano
V2 Pusubukit volcano - young dacit-andesite volcano
D1 Pardepur dacite domes
D2 Tuk-tuk rhyolite dome
HS Hot springs
Special feature: Lake Toba in "virtual photographs"
Prof. Dr. William Bowen
California Geographical Survey
10907 Rathburn Avenue
Northridge, CA 91326, USA
has kindly allowed us to publish the following three spectacular panoramic displays of Lake Toba.
THE ANDAMAN ASSOCIATION
19th February 2005
The professor has this to say on his web-site http://geogdata.csun.edu/world_atlas/index.html about the technical background of these usunusal "photographs" that are not photographs:
The technical details behind the creation of this archive of panoramic maps are fairly simple to understand. First of all, it is important to realize that the panoramas are not photographs. They are photorealistic mathematical simulations created from satellite data that have been interpreted by computer calculations. The data are derived from United States government resources available on the Web. The principal sources for topographic relief information are digital elevation models created by the United States Geological Survey or by the NASA Shuttle Radar Topography Mission (SRTM ) http://srtm.usgs.gov. Individual data quadrilaterals have been merged into larger fields, rather like a chessboard. Over this three dimensional surface is subsequently draped one or more georeferenced satellite images. Although any useful imagery can be used, my favourites are Landsat 7 (http://www.earthsat.com) and MODIS (Moderate Resolution Imaging Spectroradiometer) http://modis.gsfc.nasa.gov.
The result is a three dimensional, mathematical model over which a virtual camera may be positioned to create a single panoramic map or a series of images the may be used to create animated "flights."
Many computer applications exist that do this. My favourite is the creation of Mr. Brett Casebolt, whose company Natural Graphics (http://www.naturalgfx.com/index.htm) produces an outstanding program called Natural Scene Designer Pro. Not only is the program a marvel to use, it is the product of a creative mind that is constantly improving it. This application runs on both Macintosh and Windows computers. I prefer to use a Macintosh G4 and a G5 equipped with dual processors. I also use Adobe Photoshop (http://www.adobe.com/) for graphic editing.
I encourage all who study the earth to investigate this new way of seeing the planet on which we temporarily reside. Like the telescope and the microscope before it, this new "toy" for viewing our world from many new vantage points will reshape the way we see reality.
This atlas was created for the Web using RapidWeaver, a fantastically inexpensive and easy to use Macintosh OSX program for creating websites produced by realmac software (http://www.realmacsoftware.com/)
I am not particularly enchanted in technology for its own sake. Neither is my work supported by government agencies or private benefactors. I am a retired professor, a geographer whose goal is to see and better understand landscapes. The tools I have chosen are exceptionally inexpensive and efficient. I recommend them.
Fig. 2-3. Lake Toba today:, an idyllic scene
Fig. 2-4. A satellite picture of Lake Toba
Fig. 2-5. Lake Toba developed its characteristic geography during the last 73,000 years as shown (highly simplified) here.
Over millions of years, magma rises from below; a volcanic cone develops on the surface and this pressure rises rises until the volcano explodes in a major eruption.
(Toba: 73,000 +/- 4,000 years ago). The eruption exhausts itself when pressure from below is relieved. A depression forms which is gradually filled with rainwater and forms a lake some thousands of years after the eruption has ended.
But magma pressure begins to rise again from below and an island is pushed up in the lake. This is the situation today.
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