Photos may improve understanding of volcanic processes

Date:
July 20, 2020
Source:
Penn State
Summary:
The shape of volcanoes and their craters provide critical
information on their formation and eruptive history. Techniques
applied to photographs - - photogrammetry -- show promise and
utility in correlating shape change to volcanic background and
eruption activity.



FULL STORY ==========================================================================
The shape of volcanoes and their craters provide critical information on
their formation and eruptive history. Techniques applied to photographs -
- photogrammetry -- show promise and utility in correlating shape change
to volcanic background and eruption activity.


========================================================================== Changes in volcano shape -- morphology -- that occur with major eruptions
are quantifiable, but background volcanic activity, manifesting as small
volume explosions and crater wall collapse, can also cause changes in morphology and are not well quantified.

A team of Penn State researchers studied Telica Volcano, a persistently
active volcano in western Nicaragua, to both observe and quantify
small-scale intra- crater change associated with background and eruptive activity. Geologists consider Telica 'persistently' active because of
its high levels of seismicity and volcanic degassing, and it erupts on
less than 10-year time periods.

The team used direct observations of the crater, photographic
observations from 1994 to 2017 and photogrammetric techniques on photos collected between 2011 and 2017 to analyze changes at Telica in the
context of summit crater formation and eruptive processes. They used structure-from-motion (SfM), a photogrammetric technique, to construct
3D models from 2D images. They also used point cloud differencing,
a method used to measure change between photo sampling periods, to
compare the 3D models, providing a quantitative measure of change
in crater morphology. They reported their results in Geochemistry,
Geophysics, Geosystems.

"Photos of the crater were taken as part of a multi-disciplinary study
to investigate Telica's persistent activity," said Cassie Hanagan, lead
author on the study. "Images were collected from our collaborators to make observations of the crater's features such as the location and number of fumaroles or regions of volcanic degassing in the crater. For time periods
that had enough photos, SfM was used to create 3D models of the crater. We could then compare the 3D models between time periods to quantify change." Using the SfM-derived 3D models and point cloud differencing allowed
the team to quantify how the crater changed through time.



==========================================================================
"We could see the changes by visually looking at the photos, but
by employing SfM, we could quantify how much change had occurred at
Telica," said Peter La Femina, associate professor of geosciences in Penn State's Department of Geosciences. "This is one of the first studies
to look at changes in crater morphology associated with background and
eruptive activity over a relatively long time span, almost a 10-year
time period." Telica's morphological changes were then compared to
the timing of eruptive activity to investigate the processes leading to
crater formation and eruption.

Volcanoes erupt when pressure builds beyond a breaking point. At Telica,
two mechanisms for triggering eruptions have been hypothesized. These
are widespread mineralization within the underground hydrothermal system
that seals the system and surficial blocking of the vent by landslides and
rock fall from the crater walls. Both mechanisms could lead to increases
in pressure and then eruption, according to the researchers.

"One question was whether or not covering the vents on the crater floor
could cause pressure build up, and if that would cause an explosive
release of this pressure if the vent were sufficiently sealed," said
Hanagan.

Comparing the point cloud differencing results and the photographic observations indicated that vent infill by mass wasting from the crater
walls was not likely a primary mechanism for sealing of the volcanic
system prior to eruption.

"We found that material from the crater walls does fall on the crater
floor, filling the eruptive vent," said La Femina. "But at the same
time, we still see active fumaroles, which are vents in the crater
walls where high temperature gases and steam are emitted. The fumaroles remained active even though the talus from the crater walls covered the
vents. This suggests that at least the deeper magma-hydrothermal system
is not directly sealed by landslides." The researchers further note that crater wall material collapse is spatially correlated to where degassing
is concentrated, and that small eruptions blow out this fallen material
from the crater floor. They suggest these changes sustain a crater shape similar to other summit craters that formed by collapse into an evacuated
magma chamber.

"What we found is that during the explosions, Telica is throwing out a
lot of the material that came from the crater walls," said La Femina. "In
the absence of magmatic eruptions, the crater is forming through this background process of crater wall collapse, and the regions of fumarole activity collapse preferentially."

========================================================================== Story Source: Materials provided by Penn_State. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Catherine Hanagan, Peter C. La Femina, Mel Rodgers. Changes
in Crater
Morphology Associated With Volcanic Activity at Telica Volcano,
Nicaragua. Geochemistry, Geophysics, Geosystems, 2020; 21 (7)
DOI: 10.1029/2019GC008889 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200720112218.htm

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