The Earth Story

Maar 40 years ago this crater formed when the rock blasted itself out of the surrounding landscape. This is a maar, a hydrovolcanic crater on the Alaskan Peninsula, within the Becharof National Wildlife Refuge.

Nisyros Volcano Nisyros island sits at the far eastern end of the Greek Isles, at the southeastern edge of the Aegean Sea with Turkey being the closest landmass. It has a population of about 1000 people living on it, and a long legacy of volcanic activity.

Mývatn Maars

When lava hits water, it tends to explode. The heat causes the water to flash to steam and expand, tearing the rock apart and blasting out fragments. Those fragments tend to pile up, forming cones around the location where the water and lava met.

Those cones are called maars (or rootless cones since they’re not connected to a magma system below) and this spot is loaded with them. This is Lake Mývatn in north-central Iceland, north of the volcano Krafla. The lake originally formed in a basin left behind after the end of the last glaciation – the basin was surrounded by glacial moraines that held in the water.

2300 years ago, a large fissure eruption took place north of the lake, sending lava all the way to the Arctic Ocean. The lava flow interacted with the waters in the lake, causing explosions and forming these maar volcanic cones.

That lava flow and repeated eruptions since then left their mark on the area, producing new cones and damming the lake at different edges.

The lake is the 6th largest in Iceland. Its waters freeze over in the winter and melt in the summer, setting up a eutrophic environment with heavy biological productivity. Algal blooms form in the summer, fed by nutrients from nearby springs that supply waters that are rich in nutrients and metals due to the hydrothermal systems nearby. Diatom-rich sediments from the lake are even dredged/mined as a resource in Iceland.

-JBB

Image credit: National Geographic Wallpaper http://travel.nationalgeographic.com/travel/365-photos/lake-mvatn-iceland/

Read more: https://notendur.hi.is/~arnie/geol.htm http://www.diamondringroad.com/myvatngeology.html http://www.hafro.is/Bokasafn/Greinar/oikos_32-82.pdf http://bit.ly/1B970zY

Blasting

These rocks are the end result of a volcanic explosion called a maar, created when upwelling lava hits groundwater. The water flashes to steam from the heat, expanding and tearing apart the rocks. The largest, >5 cm chunk of rock is not an igneous rock; it’s a piece of sedimentary limestone. During the explosion it was blasted up into the air as a block that flew through the air on a ballistic trajectory and landed in loose rocks, distorting the layers below the impact site.

The eruption kept blasting out chunks of igneous rock even after the first explosion, filling in the surrounding topography with ash, lapilli, and pumice.

This site is in the Tower Hill State Reserve, Victoria, Australia

-JBB

Image credit: https://flic.kr/p/DddHF

Read more: http://www.geology.sdsu.edu/how_volcanoes_work/Hydrovolcanic.html

Aerial views of Ubehebe crater, Death Valley National Park - this crater is a maar, formed when water intersected groundwater and the explosions blasted away the sedimentary layers above. You can see the exposed sedimentary layers in the crater wall and debris from the eruptions that is now slowly falling back in.

New model for formation of Devil’s Tower (Bear Lodge)

Spattershot When the magma rising from the probable mantle plume that intersects the Mid Atlantic Ridge passed through the basaltic lump that we know as Iceland that results from this meeting and reached the surface around 2500 years before the Common Era it exploded out into the tuff ring/scoria cone in the photos. Known these days as Hverfjall, the resulting crater is around a km and a half across and is surrounded by a typical steep sided cone that is 400 metres high sitting near Lake Myvatn. Formed of layers of ash and chunks of lava that were driven out of the vent and fragmented by the pressure of expanding gases coming out of solution, it is essentially a ring of shattered debris from a lava fountain. The feature is part of a larger system known as the Krafla fissure swarm that marks an extensive weak spot in the crust that the magma forced its way through, producing a widespread set of related volcanic features from the same batch of molten rock. Loz Image credit: 1: Digital Globe 2: Orsolya and Erlend Haarberg 3:Andreas Tille https://www.icelandtravel.is/attractions/hverfjall/

Laacher See.

This placid seeming lake in the state of Rhineland-Palatinate in western Germany was once the site of an enormous eruption that spewed ash all over west and central Europe, reaching the British Isles and northern Spain. On a summer day, families will be picnicking by and people sailing on its blue waters, with little thought of the violent events that occurred nearly 13,000 years ago. The large Plinian eruption is estimated to have had a volcanic explosivity index of 6/8 (same as Mt. Pinatubo in 1991), leaving a 2Km caldera behind.

Known as maars, these bowl shaped craters form when groundwater meets rising lava, resulting in an explosion. The tuff rings from surge deposits are clearly visible at the crater's rim, now covered in forest. The eruption occurred in early summer, and the initial ash plume is thought to have risen up to 35Km high. Phreato-magmatic explosions then created pyroclastic flows and surges, that filled all the valleys with tephra within a 10Km radius, and probably wiped out most life within a circle of 50Km. They estimate around 6.5 cubic kilometres of lava were erupted. The resultant deposits are used as marker beds to correlate stratigraphy by geologists and archaeologists throughout west-central Europe.

The deposits also dammed the nearby Rhine, creating a 140 square Km lake. When the dam broke a huge flood surged downstream, leaving evidence of its passing as far north as Bonn. The phonolitic (high alkali/medium-high silica) lava had a high sulphur content, which cooled the atmosphere for several years afterwards, so the next few summers would have been pretty miserable. Among the deposits are ejecta of rare intrusive carbonatite lavas, the youngest plutonic carbonatites worldwide, attesting to some pretty complex geochemistry churning down below. Human culture was set back, as the local communities disappeared, and were replaced some years later by less advanced ones (in terms of tool quality and the like, not necessarily culture).

It is the only caldera in central Europe, as the magma chamber underneath collapsed after emptying. Located on the Rhine Graben (a downfaulted block resulting from extensional tectonics), the magma is probably related in some complex way to the collision of Africa and Europe, that also built the Alps and Pyrenees. Part of the East Eifel volcanic field, these sporadic eruptions have been ongoing for several million years, and their timing seems to correlate with the cyclic accumulation and melting of ice sheets.

The field is still active, lava is gently bubbling down below, as thermal anomalies under the lake and degassing of CO2 into the region's lakes (including Laachersee) and rivers testify. Some rare minerals were formed by this volcanism, and Hauyne was first identified in these German volcanic fields. While still active, there are no current signs of imminent eruption, and the British newspaper the Daily Mail was forced to retract a story last year that a super-eruption that would devastate Europe was imminent.

A Benedictine monastery lies on its shores (visible at the lower left of the photo), and the tuff was quarried for centuries as building stones and to make querns for grinding corn.

Loz

Image credit: IMAGE BROKER/IMAGO/SIPA

http://sims.ess.ucla.edu/akschmitt/Schmitt_etal_2010.pdf http://www.volcanodiscovery.com/laacher_see.html http://www.wired.com/wiredscience/2012/02/daily-mail-required-to-remove-laacher-see-eruption-fearmongering/

Really well shot video tour through Iceland. Some of these are areas that appear in lots of Icelandic videos, but the sea stack at about :45 in and the volcanic craters that follow, as well as some of the valleys, are places I haven’t seen featured in these and they make a great view too.

Al Wahbah Crater

Western Saudi Arabia hosts about a dozen large volcanic provinces, produced during the Pliocene and Pleistocene as what is today the Arabian Peninsula broke away from the rest of the continent of Africa. This site, known as Al Wahbah crater, is found in the youngest of these volcanic fields, the Harrat Kishb volcanic field.

That volcanic field began its activity about 1.5 million years ago and based on the remnants of early humans in the area it the youngest lava flows are estimated as having formed less than 4000 years ago.

This crater is a 2.2 km diameter hole in the ground. It is so symmetric that it was compared to the Barringer meteor impact crater in Arizona (meteor crater). Both Barringer Crater and Al Wahbah crater are found in areas with common volcanic cones, but unlike the site in Arizona this crater is actually volcanic. It is a Maar, produced when molten rock intersected groundwater, causing a series of explosions that blasted the hole in the ground. This crater was measured to be 1.147 million years old.

The crater now serves as a topographic low that occasionally partially fills with water during particularly rainy years. That water erodes sediments and salts from the surrounding walls and carries them to the bottom. The center of the crater now hosts a bullseye shape of gypsum and halite crystals from the evaporation of these occasional bursts of water.

-JBB

Image credit: http://bit.ly/1Q0ga2O

References: http://www.simbacom.com/brian/articles/SL/wabha.pdf http://bit.ly/23QavH1 http://bit.ly/1PHiakO

I RAN INTO A VOLCANO—AND LIVED!

Imagine sprinting down the edge of a steep slope so fast, it feels as if you are flying. You trip and scrape your arm, but the adrenaline keeps you going. You finally reach the bottom, take in the scene—and then realize you have to hike back up the slope of the 234.7 meter (770 feet) deep crater you descended just moments before. I visited Ubehebe Crater in Death Valley National Park in California last year at this time, and had this experience. Ubehebe Crater is the remains of a volcano that is currently inactive, so my title is not as dramatic as it sounds.

Ubehebe is 0.8 kilometers (0.5 mile) across, and is the remnant of a volcanic crater. It is defined as a maar volcano, which forms when rising magma beneath the Earth’s surface touches a groundwater source. There are also many faults in this area, which gives the magma an easier path to the Earth’s surface and to those groundwater-rich areas. The groundwater near the magma increases in temperature, turns to steam, and explodes outward due to the pressure; this type of explosion is called a hydrovolcanic eruption. An event like this destroys surrounding areas due to the debris that is ejected from the force of the explosion, and often produces a mushroom cloud. The debris from the eruption that formed Ubehebe covers the landscape near the crater site and is approximately 45 meters (150 feet) thick. The structure is part of a cluster of about a dozen such maar volcanoes in the area, and is the largest of the group.

The crater could have formed approximately 6000 years ago, when the region held more water. However, there is some debate over this number. Scientists from Columbia University's Lamont-Doherty Earth Observatory hypothesize that Ubehebe is actually much younger in age (potentially 800 to 2,100 years old), and could have formed in the dry climatic conditions that are similar to those of Death Valley today. In their study, the researchers collected exclusively surface samples with isotopes of Beryllium-10 present. This isotope is created by cosmic rays that have constantly hit the rocks, and is only present on surface sediments. From this information, the team was able to determine a potential date that the crater’s outlying sediments could have been moved to the Earth’s surface. (The movement from below would have been the eruption that produced Ubehebe.) Due to its age, this finding means that the area could still be volcanically active if there is a water source present. There are hot springs in the area, so this is possibly the case. However, this potentially volatile site also requires the presence of magma, which may no longer be in the vicinity.

No matter its age, escaping Ubehebe is no easy feat. Making your climb more difficult is the loose gravel composing the majority of the hike; for every step forward, you fall backwards two steps. My run down took mere minutes, but my ascent from the (fortunately, inactive) crater took about half an hour.

-Jeanne K.

I took this photo from the top of Ubehebe Crater in April 2012. I hope you enjoy it!

References: http://geomaps.wr.usgs.gov/parks/deva/ftube1.html

http://www.nps.gov/deva/planyourvisit/ubehebe-crater.htm

http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-16-

http://onlinelibrary.wiley.com/doi/10.1029/2011GL050130/abstract

http://ez-proxy.brooklyn.cuny.edu:2048/login?url=http%3A%2F%2Fsearch.ebscohost.com%2Flogin.aspx%3Fdirect%3Dtrue&db=geh&AN=2011-060213&site=ehost-live

http://news.nationalgeographic.com/news/2012/120125-death-valley-volcano-ubebe-crater-science/

http://www.wired.com/wiredscience/2012/01/ubehebe-crater-possibly-younger-but-no-imminent-danger-of-an-eruption/

Al Wahbah Crater

One of the natural wonders of Saudi Arabia is this volcanic crater created when rising magma met groundwater and the flash steam explosion blasted out this hole (a type of feature geomorphologists, those who study the formation of the surface features of our planet's thin crustal rind, call maars). It sits on the edge of a basaltic plateau, and represents the peripheral zone where the magma rose close to the surface without erupting. The crater is nearly 2km across and 250 metres deep. Lining a part of the bottom is a dazzling white salt flat formed of tiny crystals. The minerals (mostly sodium phosphate) were carried there from the surrounding rocks by rainwater, that subsequently evaporated in the blazing desert heat.

Loz

Image credit: Sari Sabban

http://bit.ly/1jk7L1K

A paper on the crater, paywall access: http://bit.ly/1YGLsDE