Volcanism - Debris Avalnches

Question 1

Debris avalanche

Answer 1

Large volumes >10^6m^3 and high speed mass movements that affect volcanic edifices

Question 2

Perinotto

Answer 2

2015

Question 3

2015

Answer 3

Perinotto

Definition
La Reunion Island

Question 4

Contributing factors of volcanic debris avalanches

9

Answer 4

30-45 degree hillslope
30 over max stability

1-2 m deposits

Standard weathering

Magmatic intrusions

Hydrothermal interactions

Earthquakes

Unconsolidated material composition, exposed

Steep slopes, tephra from stratovolcano

Subject to erosion

Question 5

Effects of debris avalanches

Answer 5

Trigger eruptions

Tsunami (most hazardous)
-Uzen japan 15,000 deaths 0.3km3 debris avalanche

Fluid flow, can flow over debris avalanche topography increasing danger

Larger volumes up to 40km3 for stratovolcankes

• dam rivers
• create floods

Question 6

How far can debris avalanches run out and area spread be?

Answer 6

Run out = >100km

Area cover = 1000sKM

Question 7

Case study of debris avalanche

Answer 7

Mt St Helens, 1980
La Reunion Island (Indian Ocean)
At Augustine Alaska, 1883

Question 8

Siebert, 1992

Answer 8

At Helens, 1980

1km landslide of volcano summit

Lateral blast deviated 600km pacific NW

HORSE show scar, dammed cold water lake generated flood
- drilled this to mitigate flood

Question 9

Perinotto, 2015

Case

Answer 9

La reunion Island

Largest event on a volcanic island

Accumulation of lava flows and destructive phase created gravitational instability producing debris avalanche

Question 10

Beget, 1992

Answer 10

St Augustine, Alaska
Cyclic

1883 debris caused 20km2 covering and extended coastline

2km avalanche
20 m tsunami

High eruption rates, silicic dome = over steepened and easily collapsed