L4 & 5 - Glacier Hydrology Flashcards
Give 3 water sources in glacial environments
- Snow Melt
- Ice Melt
- Rain
What are the 4 Hydrological Environments (with definitions)?
- Supraglacial (On top of the Ice)
- Englacial (In the Ice)
- Subglacial (Beneath the Ice)
- Proglacial (In front of the Ice)
What is a moulin?
A nearly vertical channel in ice that is formed by flowing water, usually found after a relatively flat section of a glacier in a region of traverse crevasses
Give 3 points about water movement in the supraglacial environment
- Surface meltwater flows down glaciers in supraglacial streams
- Water collects in supraglacial lakes bounded by ice
- Drains down moulins
Where does water go in the Englacial environment?
Conduits, cracks and tunnels within the ice – Water takes the area of least resistance
What type of river systems are common in the Proglacial environment?
Braided River Systems with daily fluctuations and high sediment load giving milky water
Why is the subglacial environment important?
- For the microbial environment
2. For glacier movement
What 3 things do we want to know about the subglacial environment?
- How much water there is
- How fast the water is moving
- Where the water is
What 4 things do we observe in the subglacial environment?
- Discharge
- Water Transit Times and Flow Paths
- Suspended Sediment Concentrations
- Solute Concentrations
What are the 8 subglacial methods of enquiry?
- Waiting for Retreat
- Hydrochemistry
- Radar
- GPS
- Satellites
- Dye & Gas Tracing
- Bulk Meltwater Monitoring
- Boreholes
What does a high EC indicate?
High solute obtained from long rock:water contact times, indicating a slow and inefficient system
EC and Q are shown on what type of graphs and what is their relationship?
EC - chemograph
Q - hydrograph
They are the inverse of one another
What are the +ves of insitu subglacial enquiry methods?
Real data with detailed measurements
What are the -ves of insitu subglacial enquiry methods?
Expensive, small snapshot and a chance that data will be missing in places
What are the +ves of exsitu subglacial enquiry methods?
Cover large areas, easy to repeat and relatively cheap
What are the -ves of exsitu subglacial enquiry methods?
Need ground truthing and it is hard to measure processes
What do observations of drainage system morphology tell us?
- Large Volumes of Water
- Channels can carve into the rock
- Channels aren’t always full of water
A channelised system is……..
Fast and efficient with low water pressure
A distributed system is……
Slow and inefficient with high water pressure
Give an example of a distributed system
A Linked Cavity System
What are the 3 types of channelised system and their characteristics
- Nye Channels - carved into rock
- Röthlisberger Channels - melted upwards into the ice
- Clarke Channels - a bit of both and unconsolidated sediments
What is required for the drainage system to remain open and not freeze over?
High Water Flow
What 2 types of information can you get from dye tracing?
- Transit time, channel full or pressurised flow
2. Dispersivity
What is transit time?
The time from injection to peak
What is a typical discharge for a distributed system?
~0.01 m/s
What is a typical discharge for a channelised system?
~1 m/s
What can happen to drainage systems over the ablation season?
They can evolve from distributed systems into channelised systems
What type of glaciers have demonstrated that drainage systems can evolve seasonally?
Alpine
What is an outburst event?
A sudden release of subglacial water with a high sediment load
What can happen as a result of an outburst event?
Meltwater can access new areas of the bed and cause drainage system reorganisation
