Options
Isotope Fractionation and HCl Partitioning During Evaporative Degassing from Active Crater Lakes
Language
English
Obiettivo Specifico
4V. Dinamica dei processi pre-eruttivi
Status
Published
Pages Number
179-200
Refereed
Yes
Title of the book
Issued date
March 2015
ISBN
978-3-642-36833-2
Abstract
This chapter provides the theoretical background and necessary practical
tools to study one of the most spectacular natural features: vigorous
evaporation from active crater lakes. We will give qualitative insights (lake
water chemical—Cl content, and isotopic composition) rather than quantify
evaporation fluxes from lakes. A major problem is that, with the current
methods, we are only able to sample the lake water, while the input fluid
rising into the lake (sublacustrine) and evaporation plume coming off the
lake remain “inaccessible”. This means that the lake behaves as a “black
box”, being the result of incoming and outgoing fluids of unknown chemical
and isotopic composition. As visually demonstrated at many active crater
lakes, evaporation is a major process. Strong evaporation from the lake
surface will affect the isotopic composition of the remnant lake water, and
the “steam devils” (evaporation plume) swirling over the lake. It is found
that the kinetic (diffusion) isotope fractionation overshadows the equilibrium
isotope fractionation effect, as a dynamic crater lake is intuitively hard
to imagine as an equilibrated system. Besides a hot water mass in
evaporation, water of active crater lakes is generally a hyper-saline (total
salinity >100,000 mg l−1) and hyper-acidic brine (pH as low as −0.5).
Although “small scale” equilibrium fractionation effects, the “isotope salt
effect” and “isotope acid effect” lead to isotopically heavier evaporation
plumes, with respect to vapor coming off pure neutral water. Besides isotope
fractionation of the water itself under such extreme lake conditions, HClgas
(and HF) will partition between the liquid and vapor phases. HCl degassing is enhanced when pH is continuously lowered by the input of acidic gases
(SO2, HCl, HF), lake temperature is higher, and evaporation is physically
favored by wind or lake convection. It is empirically deduced that HCl
partitioning into the vapor phase is chemically controlled by the lake water
temperature and density, rather than the Cl content or pH. A better
quantification of the chemical and isotopic composition of evaporative gas
plumes from active crater lakes will be of importance for volcano
monitoring when we aim to deduce the flux and composition of the “hot
magmatic end member”, through chemical and isotope budget analyses. A
major challenge for the future is to develop field methods to enable to
sample the evaporation plume coming off lake surfaces, so we can directly
determine its chemical and isotopic composition and compare them with the
theoretical approach presented in this review chapter.
tools to study one of the most spectacular natural features: vigorous
evaporation from active crater lakes. We will give qualitative insights (lake
water chemical—Cl content, and isotopic composition) rather than quantify
evaporation fluxes from lakes. A major problem is that, with the current
methods, we are only able to sample the lake water, while the input fluid
rising into the lake (sublacustrine) and evaporation plume coming off the
lake remain “inaccessible”. This means that the lake behaves as a “black
box”, being the result of incoming and outgoing fluids of unknown chemical
and isotopic composition. As visually demonstrated at many active crater
lakes, evaporation is a major process. Strong evaporation from the lake
surface will affect the isotopic composition of the remnant lake water, and
the “steam devils” (evaporation plume) swirling over the lake. It is found
that the kinetic (diffusion) isotope fractionation overshadows the equilibrium
isotope fractionation effect, as a dynamic crater lake is intuitively hard
to imagine as an equilibrated system. Besides a hot water mass in
evaporation, water of active crater lakes is generally a hyper-saline (total
salinity >100,000 mg l−1) and hyper-acidic brine (pH as low as −0.5).
Although “small scale” equilibrium fractionation effects, the “isotope salt
effect” and “isotope acid effect” lead to isotopically heavier evaporation
plumes, with respect to vapor coming off pure neutral water. Besides isotope
fractionation of the water itself under such extreme lake conditions, HClgas
(and HF) will partition between the liquid and vapor phases. HCl degassing is enhanced when pH is continuously lowered by the input of acidic gases
(SO2, HCl, HF), lake temperature is higher, and evaporation is physically
favored by wind or lake convection. It is empirically deduced that HCl
partitioning into the vapor phase is chemically controlled by the lake water
temperature and density, rather than the Cl content or pH. A better
quantification of the chemical and isotopic composition of evaporative gas
plumes from active crater lakes will be of importance for volcano
monitoring when we aim to deduce the flux and composition of the “hot
magmatic end member”, through chemical and isotope budget analyses. A
major challenge for the future is to develop field methods to enable to
sample the evaporation plume coming off lake surfaces, so we can directly
determine its chemical and isotopic composition and compare them with the
theoretical approach presented in this review chapter.
Type
book chapter
File(s)
No Thumbnail Available
Name
Rouwet Ohba HCl isot VL 2015.pdf
Size
595.59 KB
Format
Adobe PDF
Checksum (MD5)
4416724e68a094376742985b0d0bf12a