Lahars/ PDCs - merapi focus Flashcards
How can low-concentraction surges be produced (pdcs)?
They can be produced when turbulent flow pdcs overspill channels so fine material is able to flow more freely/ unconfined
How many lives were saved and how from merapi 2010?
10-20 thousand due to monitoing and warning evacuating of 20km zone
What was different with the merapi 2010 eruption compared to other events from the past?
There wasnt any difference in time between events so it wasnt a case of extra magma build up but was instead increased close surface seimicity and a much larger amount of energy relase close to the time of eruption
What was used to monitor and update the alter levels for merapi 2010?
Seismic event types - number, depth, info on magma ascent and nature of eruption
Siesmic event type - timing and onset of slides and pdcs
Gas - magma ascent,
Satellite radar - provide visual observation
Where are lahars most devestating?
when they reach lower gradients and slow down where channel capacity more likely exceeded so a greater distance than pdcs
What might be the reason that in some areas buildings were completely destroyed and some were undamaged?
Building design differences
Partial shelter by topography/ vegetation
Varaible impact duration by surge
What is the extent damage from pdcs influenced by?
size, direction and flow behaviour of the PDC.
The pattern of destruction is therefore very difficult to predict
why a large area needs evacuating
What factor was most important in aletring alert levels for merapi 2010?
Patterns of seimicity sharp increase in shallow events and onset of hybrid events before most powerful phase provided info on chnages
Why does the evacuation area have to be so much larger then the area that will ultimatley be impacted?
travel direction is highly uncertain
Why might the area affected by lahars not be the same as those affected by pdcs?
pdcs arent as wind dependent while ash and low concentraction surge pdcs which are finer grained will deposited in the direction of prevaling wind these are important for lahar generation- furthermore pdcs are relatively local while lahars usually affect areas located further from the site of eruption
How might mitigation for lahars be different from pdcs?
Pre-event warning (i.e. rainfall forecasts) and syn-event warning (upslope triggers/observation of
floods) is possible for lahars. Evacuation required along fairly narrow corridor from main channels
(limit development in these areas, with clear alarm systems and evacuation routes). PDCs much
less predictable in terms of timing, style, exact transport direction/area affected, etc.
