magnetotelluric and transient electromagnetic ... - Orkustofnun

Wameyo 430Report 21Elevation (m)W2000180016001400Menengai CratermE184159140TEM43122110TEM28TEM13TEM59 TEM4186TEM4871TEM36645953494541363127232018151232000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000Horizontal distance (m)High resistivity coreFIGURE 19: TEM resistivity cross-section EW-3Resistivity cross-section EW-3 (Figure 19) cuts across the caldera 2 -3 km to the south of EW-2. Itreveals a low-resistivity cap over a high-resistivity core. The low-resistivity cap is observed at anelevation of 1800 m a.s.l. in the westernmost sounding (TEM28). It slopes to the east but there is noindication of sloping to the west in this section. A high resistivity core is seen in the western part ofthe cross-section, reaching an elevation of almost 1600 m a.s.l. in sounding TEM28 sloping down tothe east.Elevation (m)2000180016001400WTEM11TEM30 TEM31 TEM32TEM33Menengai CraterTEM511000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000TEM35Horizontal distance (m)TEM37FIGURE 20: TEM resistivity cross-section EW-4TEM34High resistivity coreEm184159140122110867164595349454136312723201815123Resistivity cross-section EW-4 passes right across the caldera (Figure 20). It clearly defines a lowresistivitycap over a high-resistivity anomaly in the northwest part of the caldera. The low-resistivitycap reaches an elevation of approximately 1800 m a.s.l. in the westernmost sounding (TEM11), andthen shows gradual sloping to the east along the cross-section. There is an indication of the lowresistivitycap doming up in the easternmost sounding (TEM34) but that cannot be confirmed as moresoundings are needed for that. The high-resistivity core anomaly is sloping well on both sides,defining boundaries within this profile. An interesting feature is the upward doming of the lowresistivitycap almost to the surface in soundings in the middle of the caldera (TEM54 and 33) wheresurface manifestations are observed.Resistivity cross-section EW-5, across the caldera (Figure 21), shows the low-resistivity cap across thesection. It is close to the surface to the west and east of the caldera, but at greater depth within it. Thelow resistivity is underlain by higher resistivity in the western part and west of the caldera.