TUFF.. TUFA?.. IGNIMBRITE – Pyroclastic Deposits

Erosional structures at Göreme, central Cappadocia Region. The tuff is thought to have been deposited by the Mount Erciyes eruption ~2.6 ma, covering an area of about 20,000 km². This was the last of the series of great Cappadocian ignimbrites. (© Claude Valette, via Wikimedia)

In many descriptions of volcanoes and their eruption histories we stumble upon the terms Tuff, Tufa or Ignimbrite. Most every self-respecting volcano has one or all of them. Generally it becomes obvious from the context that they refer to widespread deposits of volcanic materials. But what exactly is an ignimbrite?, is it different to tuff?, and where do they all come from?

Tuff and ignimbrite are clastic rocks composed of volcanic

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Halmahera: JAILOLO EARTHQUAKE SWARMS – volcanic or tectonic?

The Jailolo Bay Area seen from the top of a hill on Manyasal Mountain. (© ftiang, via thekingdomofthisworld.wordpress.com)

When I recently noticed earthquakes listed day after day for the Halmahera region (northeastern part of Indonesia) I got my typical ‘how-come?’ feeling. So I went looking for a reason, and I read that an earthquake swarm had begun in the Jailolo region on Sept. 27, 2017. Although it has diminished by now, there are still quakes coming.

My Personal Field Trip to the Maar-Diatreme Volcanoes of the Eifel Volcanic Field (DE)

The now beautiful Holzmaar erupted 25 000 years ago. Sediment drill cores from here are used in comparative studies in both the Greenland Ice Sheet and Ice Core projects. (Photo: geopark-vulkaneifel.de)

A maar is a hole in the ground, of volcanic origin… what else?… caused by interaction with water… That was about all I knew about maars when I prepared for this year’s holiday, in the German Eifel maars area (Vulkaneifel, Rheinland-Pfalz district). I did not expect to find a great lot of evidence for former volcanic activity. Probably all covered by sediments or eroded, mined away or grown over – that’s what I thought. Mind you, it was not the famous Laacher See caldera I visited which had produced a VEI 6 eruption some 13 000 years ago.

BATHOLITH…, LOPOLITH…, SILL OR DIKE? – INTRUSIONS (2)

INTRUSIONS PART 2: INTRUSIVE ROCK FORMATIONS

Elephant Rock (NE Lower Austria) is an outcrop of the South Bohemian Pluton (central Europe). This batholith is one of the largest intrusions within the Variscan (or Hercynian) orogeny, with a surface of ~6000 km². The rounded “elephant” shape of the granite blocks is caused by spheroidal or woolsack weathering. (© Isiwal, via Wikipedia)

GRANITE…, SYENITE…, DOLERITE… INTRUSIONS (1)

INTRUSIONS PART 1:  INTRUSIVE IGNEOUS ROCKS

Stone Mountain is a part of the Spruce Pine plutonic suite in North Carolina, U.S.. Petrologically, “the marginal phases are fine- to medium-grained muscovite-biotite tonalite to granodiorite, and the interior of the pluton is largely medium- to coarse-grained leucocratic muscovite-biotite quartz monzonite to granite”. Not that complicated, or is it? (© Nathan Lyons)

Magma is intruded somewhere deep down, it stays down there, it cools down there, never to be seen for the next couple of million years – why should anybody care about it? Well, as we’ll see, in many places it DID come up. In fact, a good percentage of Earth’s surface is made up of intrusive rocks.

Basaltic…? Felsic…? Porphyritic…? Confusion!

Felsite quarry at Mount Ararat (© en.ararat-stone.com)

That’s how I felt at times reading interesting things about volcanoes but had to skip those -ic words. So, I am trying to give you a simple overview on rock types produced by volcanoes… I can already hear the experts groan: omg, “petrology” and “simple” are the two most antagonistic terms in the world! 😉 Nevertheless, I know all too well our typical skip-and-jump motion when it comes to different lavas, just let’s try and achieve a broad understanding about what volcanoes bring up from the depth.

What is a low velocity zone and why should I care?

Schematic of low velocity zone http://www.iris.edu/hq/files/workshops/2012/06/docs/scihi/WebPages/0006.html

Nothing left but a stopper… – Volcanic Plugs

Shiprock, from the air, 2012 (© Doc Searls, via Flickr)
The author’s description reads: Shiprock ( or Tsé Bitʼaʼí, “rock with wings” in Navajo), is a monadnock or inselberg – in this case a volcanic plug, standing nearly 1600 feet above the surrounding desert in San Juan County and the Navajo Nation in New Mexico. Formed about 27 million years ago, during the Oligocene epoch, Shiprock was once a vast and broad volcano, now eroded to its deepest hard parts. Its peak is 7,177 feet above sea level, and it is the preeminent landmark in northwestern New Mexico and the Four Corners area. It is also sacred in the Navajo people. Climbing, once done often, is no longer allowed.

Valles Caldera – Jemez Mountains

A view from the southeast to the northwest across the Valle Grande and Redondo Peak. Image: from 2011 Nature article.

What are the tectonics behind Rinjani?

Google maps of Lombok island with Rinjani and Tambora to the east