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Earth of fire

Actualité volcanique, Article de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #Actualités volcaniques
  The Mono Lake and tufa towers - photo Nasa Astrobiology research area.

The Mono Lake and tufa towers - photo Nasa Astrobiology research area.

A new technique has been used by USGS scientists to model the magmatic system beneath the  Mono craters and Mono Lake, located northwest of Long Valley caldera / USA.

The magnetotelluric technology  measure the small electric currents naturally created by the movements of ions in the Earth's magnetic field (like the Northern Lights).

The flow of these electrical currents through the rock varies with the composition and other properties: the older, dense rock deep seated are more resistant to the electricity passing through them, while fractured rocks containing fluids, including groundwater or hydrothermal fluids related to volcanic activity, are less resistant. The magma chambers containing molten rock boiled or partially crystallized, have a resistivity even lower.

Landsat satellite image of Mono lake and Mono craters to the south of it - the analyzed area occupies the upper left corner of the simplified geological map / doc. Long Valley caldera USGS - Lyn Topinka
Landsat satellite image of Mono lake and Mono craters to the south of it - the analyzed area occupies the upper left corner of the simplified geological map / doc. Long Valley caldera USGS - Lyn Topinka

Landsat satellite image of Mono lake and Mono craters to the south of it - the analyzed area occupies the upper left corner of the simplified geological map / doc. Long Valley caldera USGS - Lyn Topinka

The analyzed area includes the Mono Lake, with Paoha island, an intrusive rhyodacitic dome (a cryptodome) that emerged in the middle of the lake due to its activity here about 350 years, and Mono craters, with among others the Panum crater, which last erupted 600 years.

On the northwest shore of Mono Lake, Black Point, a basalt cone dated to 13,300 years form the most prominent structure in the area. Spectacular tuff columns adorn the southern shores of the lake.

Mono lake and Pahoa island - Miller / USGS Photo

Mono lake and Pahoa island - Miller / USGS Photo

3D model showing resistivity anomalies under the Mono craters (in order to NO) - Doc. USGS

3D model showing resistivity anomalies under the Mono craters (in order to NO) - Doc. USGS

Geological model of the region lake Mono / Mono craters based on 3D imaging - C1 and C3 are partially crystallized magma columns; the connection C1-SC / South Casting - the connection C3 - NC and PC / North casting and Crater Panum; C2: fractured zone containing fluids; R1 cold pluton; hatched lines correspond to a faults modelisation: LVF / Lee Vining fault and ISF / Indian Springs fault. - Doc. USGS

Geological model of the region lake Mono / Mono craters based on 3D imaging - C1 and C3 are partially crystallized magma columns; the connection C1-SC / South Casting - the connection C3 - NC and PC / North casting and Crater Panum; C2: fractured zone containing fluids; R1 cold pluton; hatched lines correspond to a faults modelisation: LVF / Lee Vining fault and ISF / Indian Springs fault. - Doc. USGS

A new 3D image of the magma chamber and plumbing underneath the Mono Basin should provide a better understanding of the future : size, shape and location of the place of a future eruption.

Resistivity studies reveal the presence of two almost vertical bodies under the SE and NE of Mono craters edges, at a depth of 10 km. These bodies are interpreted as zones containing 15 ± 5% of molten crystal slurry, surrounded by hydrothermal fluids, and likely the source of eruptions dating back to the Holocene. Two conductive structures seem to link each magmatic source to the surface; the magmatic body located further north is connected by an arched structure to  vents close Panum Crater, where high conductivity suggests the presence of hydrothermal fluids.

A third structure, characterized by a lower conductivity (4-10 Ω · m) extends 15-35 km depth, from the western Mono craters up to the east front of the Sierra Nevada, and corresponds to a zone marked by sporadic LP earthquakes , characteristics of a fracture network completed by metamorphic or magmatic fluids.

Between these structures, under Aeolian buttes, a different resistivity zone (between 103 and 105 Ω · m) corresponds to a granitic cold pluton plunging up to 25 km. below the surface, and controlling the arcuate shape of the Mono craters chain.

 

  Mono lake & craters - date of the eruptions - doc. USGS

Mono lake & craters - date of the eruptions - doc. USGS

The Mono craters volcanic chain - photo Dan Mayer

The Mono craters volcanic chain - photo Dan Mayer

 Panum crater - rhyolitic obsidian - photo americansouthwest

Panum crater - rhyolitic obsidian - photo americansouthwest

Sources :

- USGS – 3D images of magma below Mono craters area - 29.10.2015 - link

- Global Volcanism Program - Mono craters

- USGS - Long Valley Observatory - link

- Indiana University - The Mono basin :  history of extremes - link

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